This is a really cool site for catalogs on the Miyata's; see: http://www.miyatacatalogs.com/2007/1...alog-1981.html Just click on your year and scan down. If you compare the picture and spec'd parts to yours you'll find out quickly how original it is. Right off the bat the handlebars and stem are not original, if you want to restore it you could locate originals for not a whole lot of cash. Getting the bike back closer to original condition would make the bike worth more if you plan on flipping it.

I own 2 Miyata's myself, my first one I bought new in 87 a Team model, then about 8 years later I found a nice condition used 88 Miyata 712 at a garage sale. Personally I think the models they made with the splined triple butted tubing was the best tubeset made back then by anyone.

I too think the 612 is probably worth around $400 depending on condition.