Took fac air out of 1971 442 (455 motor) will non fac air heater box fit or do I have to order AC delete cover from OPG

 

If the factory non-A/C box fit, there would be no market for the aftermarket part.

Yes, the firewall cutouts for A/C are much larger than the ones for heater-only.

And keep in mind that the heater-only box is cable operated. The A/C box is vacuum operated. The A/C delete retains the vacuum operated part under the dash so you still have heat and defrost. It only deletes the A/C evaporator under the hood.