Does anyone know where I can find information about Miyatas? Basically, I am looking for information about models and years, the specs, geometry, components, etc.

The reason I am looking for this info is that I saw an ad for a 1990 Miyata 310. The ad said the bike was an aluminum frame. I would like to know if this is accurate or if it is a steel frame and if steel, what kind. I would also like to know what is on it.

There was no model 310 in 1990. The last year that this model existed was 1986. There was quite a bit of variation on this model, depending on exact year, but in general it was a lower mid-range model. The frame was always CrMo but early years were plain gauge, later being upgraded to double and finally, triple butted. Forks on early versions were hi-tensile with later versions being Mangalight. Geomtetry was club racer/triathlon. Prior to 1984, components were SunTour/Sugino/Dia-Compe mixes. In 1983 and later, , the mix was typically Shimano 105 derailleurs with SR cranks and various brakesets. The only year to feature 700C wheels was the last one. You really need to ask the seller some specific questions. Do you have pics? I can probably identify it from one.

Good to know about the year being wrong. I guess that is why I couldn't find any info on it with Google.
I was going to ask some questions, but I wanted to get the general information about the bike first to see if it was worth my effort/price. This is an eBay item with not very good pictures.
eBay Miyata

But if the sizing is correct, then it would be the correct size for me, if the top tube is long enough. I prefer about a 53 cm top tube.

The pics are very bad. You can't readily identify any of the components. Assuming the seller has the model number correct (which may be jump in faith, as just about everything else is wrong) the color scheme makes a 1986 model. That means a triple butted CrMo frame (not hi-tensile) with Mangalight forks. Shimano 105 derailleurs, SR SUC-100 crankest, Shimano Z-series brakes, and Shimano hubs laced to Ukai 20A (700c - they got that right!) rims. Advertised weight was 24 lbs (21 lbs would be a stretch even with the small frame) . I don't have the 1986 pricing but the 1985 version was $300 US, so figure about the same.

That appears to be the 50cm frame (Miyata measures ctt), in which case, the top tube should be 53.5cm. Hopefully the seller's obvious ignorance and numerous errors will scare off any potential bidders.

I was hoping for the same idea about repelling buyers. Thanks for the help, I'll email the seller and ask for better pictures of the components and any decals.