I was actually inquiring about the Vintage air setup. I am wondering how easy a heater/evaporator box replacement for an early Mustang would fit.
Don't know, but if I get a chance, I can pull a 69 Mustang hvac box, and take a look. (Parts cars are nice to have) Edit: on second reading of your question, to my understanding the vintage air kits for mustangs are the same main box, but with different accessories for the specific model. IE: the GenIV main case may be used, but with a kit for dash vents, or adaptors for the controls.