Hello.
First let me apologize for being so uninformed. I did try to read sheldon brown on the subject but still have a couple of questions, so here goes, and thank you in advance.
I have an older road bike and the fork is pretty rusty on the insides of the blades(?). Not the inside of the tubing mind you. Maybe the best thing to do is soak it in that oa stuff you guys talk about. But I've never been attached to the fork because I'm pretty sure it's not original.
So my main question or questions, if anyone could be so kind as to enlighten me, are:

If I were to get a new fork would it be wiser to find the 1 " threaded which I assume my bike uses(late 80s ish rossin) and if so where is ebay my best bet.

Or

Is it possible to get a newer fork hs and stem and afford myself a little more fit customization?

Thanks again

As always, photos will go a long way to helping us help you. One concern I have right away, since you suspect the fork is not original, is whether the frame has been damaged, as well as the original, discarded fork, due to a crash. Photos exactly perpendicular to the plane of the frame will help rule this in or out, as well as close-ups of the down tube and top tube near the head tube. Check especially for dimples in the tubes, and cracks in the paint in these areas.

Looks like a job for sandpaper and a rattle can of grey primer to start...

Get the rust off and inspect... Don't be afraid...

I'm sorry for the weird pics. Wife out of town and the only camera is a front facing nexus camera lol. This is as good as is gonna get for now.

There's the whole bike.

that's a sweet looking Rossin you've got there. and DA 7400 components! dunno much, but seems having lotta potential.
to my untrained eyes, the fork does indeed look "not original".
generally 'newer, more modern', not complimenting the beautiful lugged frame much, unfortunately. (that's just me)

the rusty freckles on the chrome—also hard to tell from the photos as is—don't look too bad, tho.
try rubbing using a handful of cooking foil ball dipped in vinegar. most of the time, it works like a magic.
if not removable in that way, that's a good sign of having to move onto the next level—such as OA etc.

btw, the saddle tip angle seems hung up on a pretty uncomfortable level, no?

what do i know... congrats on getting a beautiful frame!

Seat yes. I was messing with it before work to try and get it further back and ran out of time. Work by the way is 5 miles with - 700 ft elevation change... Coming home is intense. Duluth mn

If you decide to junk the old fork, there are lots of replacements new, used and NOS on eBay. You could even go carbon if you want; that's a pretty 'showy' bike and it wouldn't look too out of place.

Anyway, as you probably already know, the important measurements are the diameter and length of the steer tube. I'd just remove the rust, buff it smooth with 1000 grit wet sanding paper and give the fork a good waxing every now and again to keep it from getting rusty again.

yep it's a cheap-ish Taiwanese unicrown fork and probable cause is just thin chrome plating (and plenty of exposure to weather). If that was my Rossin, I'd want a nicer (chrome) fork...but this one looks like it works.
Measure the frame's headtube and that will give a rough number of how long (tall) a steerer you need...I probably don't have a spare with a long-enough steerer, but somebody here might.