So how hard is it to add A/C back in the car?

[Longroof79]

In my opinion, with what he has (assuming the parts he has are working), then it would be much more cost effective to just get the missing parts. I'd only suggest going completely aftermarket if everything from the OE system is already gone or your car is already stripped. The interior is out of my car and I'm taking out the dash pad, so now is the time to get a new aftermarket system, but with a trans, rear end, and fitech up first....we'll see how it goes.

Using the original HVAC box and some components. It would not be a bad idea to go with a new Sanden compressor and brackets. I think the Sanden unit will outlast the R4. I know I should've gone in that direction.
A few years back one of our members went with a complete Vintage Air conversion. That entailed removing the HVAC box and installing the smaller aftermarket unit inside the car.
It, of course cleaned up the firewall. It took some creativity on his part being that the unit was universal to be used in streetrods, etc. The installation came out quite nice, too.
It also involved removing the dash.