Stamped dropouts with eyelets, no bottle bosses, clamp style shift levers, swaged crankset, brake safety levers,nutted axles and exposed brake mounting nuts are all indicators of an entry level model for the early to mid-1980s era that it appears to be. The frame is almost certainly hi-tensile steel.

Personally, I'd be minimizing the upgrades. Enjoy it as the commuter you intended it to be.