Hey Paul,
I try to look at this stuff on a part by part basis.As far as the radiator I assume they are asking because with A/C You want maximum cooling,personally I like maximum cooling on everything so I always go with the better cooling radiator within reason(cost). As far as a heater cores cars with factory used A/C Used a different heater core than cars without it . This started in 67 so you would want to try and id which heater box you have? Does your car still have most or all of the original A/C Pieces?