I hope I am posting this properly and in the correct section of the forums. If not please let me know.
Can anyone tell from the photo if this is the correct size frame for me? I have the seat post adjusted so that when the heel of my foot rest on the pedal my leg is nearly straight. Seat tube measures just about 21 inches.
I recently posted in this forum that I was looking for a 22 inch or 56cm lugged steel touring frameset. My thinking is if I go with a frameset 1 inch longer than this bike than the hanlebars will be higher in relation to the seat. Bending over to low bars has become too uncomfortable in recent years.
But if I did go with a 22 inch frame I am assuming the top tube will be longer and the reach to the bars will be longer and somewhat cancelling out the benifit of lower seat/higher handlebars. I have installed a longer stem to riase the bars on this bike and it has helped with the comfort and enjoyment.
My apologies for the cluttered photo. Please let me know if a "cleaner photo would help".
The hassles of an aging body, I had no idea it was going to be so much work to get old. I know realize why folks retire from their jobs, getting old takes all one's time.
As always, thanks for your help.

Not an expert but it looks okay to me. Also, I think they made frames in 2" increments, so I don't think they made that one in 22", though other manufacturers may have had 22" ones.

A lot depends on how comfortable you are to having the top tube in close proximity to your naughty bits when you stand over the bike. I like to have my top tube grazing my shorts when I stand over the bike, but not pressing on anything delicate - touching yes, pressing no; I don't want every stop sign to be a potential nut shot.

To my eye, your current set-up looks like the frame is a bit short for you - perhaps 2cm to 4 cm. But the standover test will tell you more than my eyeballs can from 3,000 miles away.

Your reasoning is sound. Larger frames raise the top tube and make it longer. It looks like you've already chosen a pretty short reach stem, and you're using swept back bars. Some people have back pain from such an upright position, but if it's comfortable for you and not causing any problems there's no reason to change it. If you're at the height limit of the stem you're using, a larger frame will let you put the bars even higher. The effect that has will vary from frame to frame. Different manufacturers have different sizing philosophy. Some increase the top tube length proportionally to the seat tube size, but some don't.

If you have medical insurance, it might be worth seeing if your insurance will cover a bit fit.

+1 on maybe too small. It is your ride and you ride differently than I do. I ride drop bar bikes and a short frame can lead to neck and shoulder issues for me. On an upright type bike it can work if it is comfy. I ride a 62-64cm bike and also have a couple that are 60cm. I can ride the 60 cm bikes for 2-3 hours max, that’s it , so they are my 30 mile bikes or quick blast to the harbor for lunch bikes.

A lot depends on how far you're riding and how much peddling efficiency matters. Getting near full extension on the pedals is most efficient, but I've found that a smaller bike works better for me when I'm just noodling around town and not trying to go fast. My road bikes are around 25 inch seat tubes, but my bikes that are set to ride upright are more like 23 inches. When you're stopping frequently at intersections, I think being able to get solid footing while seated matters more than getting full pedal extension, and as you said, you don't really want any additional length.

The current sitting postitioin does not bother my back. On the other hand when the bike still had it's original drop bars that riding position was uncomfortable for my hands, wrist, and neck. I would like to try to get back to a drop bar bike again and was hoping that a larger frame with a tall stem would allow that.
My wife and I ride a Burley Rock and Roll tandem with a 22 inch stoker seat tube and 26 x 1 1/2 inch tires. Standover height is no problem. The reach to the upright bars feels OK but not perfect.

I ride upright and have gravitated to larger frames as I age. I used to ride a 23" frame always. My minimum these days is 23.5 and a routinely ride 24.5. I do need to be careful when stopping but I just stand in front of the seat.

My 24.5" frame.

That's a tall stem, but with a short reach.

You could probably use a frame that is slightly taller, but the larger frames are typically also longer. Make sure that is what you want.

I have mixed opinions on bikes with sloping top tubes, but this may be one of the reason that the more modern bikes have the sloping top tubes. So you can get a comfortable seat height, without having a stem that is a yard long.

Is the frame too small?. Well that depends on what you want to do. I´m 180cm, and so a 56cm frame should in theory be pretty much perfect for me. But being in my mid fifties, the sad truth is, that I get neck pain on longer rides, when using 56cm frames with drop bars. The reason for that, is probaply, that I prefer to be looking through my glasses, instead of over them. My favorite drop bar bike is supposed to be 58cm, but according to my measurements it´s actually closer to 60cm. This size gives me a fairly upright seating position, and this means that the only thing that hurts on longer rides is my butt!.
My winter/beater/grocery getter is an old Centurion that is around 53cm, and set up pretty much like your Miyata. It is actually a very comfortable ride for me, and surprisingly fast, actually it´s not much slower that my other bikes, if I put similar tyres on it. With drop bars that bike is absolutely unacceptable to my neck. So apart from looking silly (Just like your Miyata), that small frame is fine.
Based on my experience, I´d say, that if the Miyata is comfortable to you as it is set up, I think a 56cm or even possibly a 58cm frame would probaply be a good idea if you want drop bars and a fairly upright seating position. Of course a frame with a not too long top tube, would be best for this application.

For a proper internet fitting, we need a shot of you on the bike. 😉

I imagine that if you regularly ride a recumbent, reaching for drop bars will feel odd. Nice build on that Miyata by the way. Find another larger one, put drop bars on it, and when you are not riding with your wife on the tandem, only ride the new bike with drop bars. Your body will adapt.

Size looks fine to me.

BITD steel, lugged production frames were made in size increments. For the American market, less expensive bikes were made in 2" increments, more expensive ones came in 1" increments. When I was younger I was a "tweener", best fit was 24" measured center to center (CTC). My first "real" bike was a Raleigh Super Course, and my choice was 23" or 25". Technically Raleigh made them 23 1/2 or 25 1/2 center to top (CTT). I was 15, so the dealer assumed I'd grow more and got the 25" frame, which I happily rode for years, including a couple of tours down the California coast.

I'd agree with those that say that frame is on the small side for you, but if you enjoy riding it, and the riding position works for you... On your next bike (you do plan on having several vintage bikes, no?) look for one a bit bigger.

Like others pointed out - these frames frequently came in 2” increments. The next size up will be too big.
Right now the only issue is that the tall, short reach stem looks goofy. This is purely a looks issue. I would swap to a shorter stem with high rise bars.

To clarify my "it looks a bit small" comments earlier, I was talking about the OP's stated desire to perhaps try drop bars again. For that purpose, I think the Miyata is a bit small. The bike as currently set up looks okey-dokey to me - there is more margin for error with upright bars, especially swept back upright bars, than there is with drop bars. And it looks good, .