What year is your car? Does it have H51 on the fender tag? (that's the code for AC) Does the VIN on your dash pad match the one on the fender tag? If your original dash pad has been swapped out for another one, it's a really good idea to check and make sure you have the right VIN on there. Compare with radiator support # & cowl #.

If you'd like to post your fender tag info, we can do a complete decode for you and you'll then know for sure what you're working with.

I've changed a NON-AC car into an AC car before using all factory parts. It's a lot of work, but can be done.

The windshield defogger ductwork is different for AC cars, so test fit yours with the AC box installed to see what you've got.

If you're going to run a rallye dash, you'll need a rallye dash AC control. That might be a tough find.

you'll need an AC dash pad, right & left AC ducting, and AC vents. There are some small differences in the AC vents (width of white stripe, ridges on directional adjuster tab, rubber flap to close vent) you might want to make sure you get a matching set.

AC cars also had a long skinny plastic trim piece that mounts to the bottom of the dash frame to help hide the AC box from sight. It's not necessary if you don't want it, but it would have had one originally.

You mentioned the car was a rallye. That would make it a 72-74 challenger. Since those cars didn't come with 440 4 barrels, I'm guessing you're going for a custom thing, not an all original look. If that's the case, I'd reccomend the Sanden compressor over the stock unit. The Sanden takes 9 times less horsepower to operate. Whether you use V or serpentine belts is still up to you.

Tav