Try the Retro forum at www.roadbikereview.com (sorry to plug the competition, but that group has been helpful). You might be able to steel wool or scrape off the primer to reveal the original paint, so you could read the lettering. If not, you could post the type and model of components, so we can at least get an idea of when it was built and how expensive it was originally.
I don't remember when six speed freewheels replaced fives, but I think it must have been in the mid to late '80s. Other clues would be the location of the shifters (on the downtube generally means a better bike than long levers on the stem), whether it has "safety levers" so you can operate the brakes from the top of the handlebars (cheaper bikes often had them, more expensive ones didn't), whether the dropouts (the places on the frame where the axles mount) are forged or just look like pieces of stamped, flat metal welded onto the fork and the rear triangle (forged is better) and whether the wheels are steel (cheap) or aluminum (more expensive, though I think by 1985 or so most bikes used aluminum.