I'm only going on the decals which are pictured above. However, notice the Dutch (?) under the "100." Does the serial number provide any clues? UB00141

I saw the serial number on the upper head leg in the original set of pictures but could not read it. It indicates that the frame was manufactured during the 2nd fortnight of 1992. So it would appear that the decal signifies the company is over a century old and not that it's a centennial model.

I'm pretty sure that's not Dutch.
A quick google translate suggests it is Swedish... and leads me to a couple of our Swedish members.
Which roughly translates to:
Reminds me of [MENTION=500982]Rodrider88[/MENTION]'s 1987 Miyata 1000 for the Swedish market as well as the 1990 Miyata 1000 from [MENTION=497429]Patson[/MENTION].
They had different colours and sometimes placement of the cantilever brakes from the American models.

Hi, that’s swedish and almost all Miyata bikes in Sweden had that sticker from 1990 and forward. The Valley Runner in the swedish Miyata catalog from 1993 looks almost like yours except for the valley runner sticker on the top tube that is in red.

Another solid option is to have someone build you a frame and buy a fork for it. Down in KY, (or Stateside) there has got to be some amateur talent who could knock something together for you. I'd like to build a frame; sort of a short tail cargo bike type thing.

I ride the Raleigh Elkhorn, which is a 23"/23" IIRC. The other bike, the SM600, is their extra large with a chimpanzee-ish 24" top tube (aluminum though). I haven't even ridden it yet after almost 3 years owning. There has to be literally hundreds of different old steel frame mountain bikes which have been made in the past. Lots to choose from.

I bought this last Saturday because it's tall and I'm an addict. Advertised as a 20'' size.
Seat tube is 615mm ctc, 640mm ctt, 35'' stand over. 36.7 pounds as pictured. 9.37 pounds frame, fork, and headset. Stem is 1.4 pounds.

Wanting a winter beater so you know how it goes.

The largest vintage mountain bike i have owned is a 24" Univega Alpina Country. I no longer own it because I went to all 700c bikes.

I wonder how a Swedish Market Miyata found its way to a thrift store in the pan handle of north west Florida?

So with that seat tube length, the frame is a 24" size?

That looks perfect. I'll keep my eyes open.

Yes it’s exciting how it ended up there. It may have come with a moving load from Sweden, are a few thousand swedes who move to the US every year.

+1. While I can't read it from the picture, it's not Dutch. If it was from the Netherlands, it would be branded Koga Miyata. The Swedes, and possibly the rest of Scandanavia, were a different market with their own importer, who tailored the bicycle to local preferences. Consequently, like the Koga Miyata, they often don't match the USA models.

quick note about sizing on these too. The seat tubes and head tubes will be a lot shorter than you would expect from a road bike. Vintage mountain bikes in the 80s ran a lot of seatpost stem and used riser bars. It's something I didn't figure out for a while. For a while I was chasing larger and larger mountain bike frames but it was because I was thought running a lot of post and needing a lot of rise via a tall or more upright stem meant it fit badly. This sizing was by design. And the top tubes on these can be very long. Some of them ended up being very long because they cross country racers became more stretched out and agressive over time. Good if you have a long torso, a little tricky if you have long legs like me and are running drop bars.

Example of mid 80s geometry. Source: https://mbaction.com/whats-the-most-...-of-the-1980s/ Btw, Rockhoppers are also great frames and don't have the price tag of Stumpys. Drop bar example: Show Your Vintage MTB Drop Bar Conversions

I believe this was the only Ross ATB offered in this large a frame and that the others were about 5cm smaller, for the biggest frame.

If one wanted to find a new frame that fit the bill here, Handsome Cycles is offering a Bridgestone XO reproduction frame for $699 in a kickstarter campaign. You get your choice of three colors, four sizes and a headset for that price and it will be delivered in July. I kinda like it but in keeping with the original design, they are limiting the tires to a max of 26X1.9. If it were bigger, I would give it more serious consideration.

The kickstarter campaign has reached the minimum and it lasts until January 1 if you are interested.