Should I Replace AC Condenser?

Since you're strayed from 100% original, install a dedicated, R134a specific condenser for your car, if one is available.

If you re-use the OEM R-12 condenser (if it's still usable), you're going to have issues with refrigerant charge and system capacity/performance (head pressure issues, inadequate subcooling= less capacity, etc). I'm not saying it can't be done, but it's going to be a headache from Day One.

Been there, done this several times, and learned from experience.