I have some spare non-A/C parts left over from converting a car back to A/C that had been removed years ago. Underdash box etc. The problem is that the cutout in the firewall is different for A/C vs. non-A/C (different size, shape and location) so no matter what you do you will need to make some modifications.

Heater control is different, wiring harness is different, blower resistors are different. It is not necessary to replace everything with non-A/C parts but you will need to do some work-arounds, some of which are relatively hard to reverse.