The non-A/C heater box for the firewall side will not fit. The holes for the heater core are different and the rectangular hole for the unit itself is different. The inside heater portion is different on the A/C car as well - also due to the difference in heater cores.
If you are set on removing the A/C box on the firewall side, then you can always weld in a plate to cover the holes in the firewall and not run any type of heater or you could install a Vintage Air System.
If you decide to go ahead and remove the A/C box with evaporator on the firewall side, I will buy them from you. I am missing that on my recently purchased '69 convertible.
