I seriously doubt that you have read the posted links to sheldons site as they should have answered your question.Anyway...let's say your Schwinn is the right size,look at the dropouts(thats where the rearweel is attached)then compare them to the Pics on sheldons site(horizontal).Then look at the crank..is it cottered(a "bolt " goes thru the crankarm at the spindle,is it a single piece crank(the crankarm goes thru the BB shell in one piece).If it is ..keep looking for another frame.As the tubing goes ...a higher end tubing set is nice ,but for your first build a Hi Ten steel frame should be good enough to start with.Just don't pay too much for it(i've gotten some for $20 or less).