I agree with JeepcoMJ, however you will not need to replace evap, I do however recomend that it be flushed as well as the rest of system, but if parts truck a/c is still closed and you CLEANly take it apart and plug holes and spill no oil you should be fine. I do think you should replace any o rings you take apart and even though this is a r 12 system they adapt to r 134a just fine, don't mess with changing oil or fill fittings. just use a r 134a side can tap will acme r 12 fitting and fill her up, I'v done this to many a/c systems and have never had any problems. That's my two cents
TRavis