What years were the heater boxes interchangeable in these trucks?
I have a 78 that someone did a heat delete in and I have to start gathering parts to put it back. There is a big hole on the firewall with a makeshift plate over it. Does that mean it was a factory air truck?

 

Big hole big enough to crawl thru.... Yep Factory air. I think you could use a non-air box and fab a special cover. This would allow you to replace the heater core from the engine side....

 

I would love to put the air back. Now that would be killer !! Wonder if there are any fitment issues with the 429 swap and factory air?

 

I fit that ac box in my 64 with a 460 shoe-horned in and it fit.... I'm sure someone will come along who has done that 400/460 swap that had factory air. They will know for sure. It does make getting to the rear plug on that side interesting but doable.

 

Visit these guys' Nostalgic Air Parts using the link below and I'm confident you'll find a system for your rig:

Aftermarket Air Conditioning For Automobiles and AC parts

 

My truck had a 400 with air factory, so ya they fit. Fits with the IDI in there even. Although i cant get the valve cover off with out taking the box apart.

 

i had a 76 with a 360 and my brother had a supercab with a 460 so it will fit factory air