Generally chromoly is gonna be decent. Looking at the dropouts is really the best way for a newb to tell the differance. Also shifter location. Downtube good.....Stem bad. For the most part anyways. Bar end shifters can be a good thing too. Brake levers with those silly levers that are generally called "suicide levers" are a pretty good indication of a low level bike. There are always exceptions to the rules.
As far as components are concerned. Yes. For the most part it is very easy to upgrade them if need be. This area gets a little fuzzy when dealing with older French bikes among others but Japanese bikes are pretty much all standardized so swap away! If you find a listing that interests you on Craigslist or something go ahead and post it up! The peeps in these parts are a friendly bunch and we'll be glad to help steer you in the right direction. Might be worth it to post in the ISO/WTB section here in C&V too. You never know! A member may be local to you and could help you get hooked up.

Kelly D