Vintage road bikes from Japan are for the most part a decent bike. Steel frames make for a smooth ride for they absorb the bumps better the aluminum and carbon. ( of course all bikes under a Brooks saddle are comfortable) I can go to a couple bike shops and get new 27 inch tire. I seen them even at Kmart and that other place when forced to go. So if you see a old Schwinn in good condition and at a decent price go ahead and check it out. If you live in my neck of the woods where everyone thinks thier vintage bike or used newer bike is worth so much more then I would ever buy it for, and unless you're seven feet tall good luck finding a bike at a good price. Which brings me to Bikesdirect.com.
I bought a Dawes roadbike from them for 400 bucks and I owned it for a few months now and Im quite pleased with it. They're right about the tires. POS for sure. But I'm still riding on mine and the only thing I replaced is the saddle. (can you guess with what?). And even before the switch it really wasnt bad on bumps for a aluminum frame. For positive sizing contact BD before you order!! Tires will need to be Trued and the rest you can probably put together yourself. It isn't rocket scientist. Might need some cable adjustment. Get a book or watch a few YouTube videos to see how it's done.
But do check out the classic and vintage forum for sure before you decide. Old bikes are the best bikes.