miyata what?
 

Hi guys, newbie here. stuff: 1983 Bianchi sport ss; 1985 Bridgestone mb-3; 2006 Raleigh comfort/hybrid thing with a big soft saddle.
I'm looking to buy this Miyata. I think it's a 910 or 710 from the mid 80's but it's been repainted, over decals and all - shimano 600 drls, brakes, cranks. Serial # n30268. Any help greatly appreciated, thanks.

What "help" are you looking for exactly?

I suppose you are trying to date it and figure out what you have.

Easiest thing to do is date the parts.
http://www.vintage-trek.com/component_dates.htm

Once you have the build date then you can look at the corresponding catalog and match up the parts to figure out the model. If the parts are dating late in the year the bike may be the next year model.

http://www.miyatacatalogs.com/

That's not the Miyata serial number format. Either you're missing a letter or it's not a Miyata built frame.