I run this one in my Cuda. It's internally regulated to 7 psi so you don't need a regulator. I'll try to get some pic.s later. http://www.summitracing.com/parts/HLY-12-125/
I think a reverse manual would be a huge pain on the street. Especially if you're trying to use it with a slap stick. All you would need to change is the valve body to make it fwd pattern.
Drivers side dash right where the dash meets the windshield. Maybe you should just ask the owner what the story is with the car instead of sneaking around. Just a thought.
Sure looks like a nice car to be cutting up but I'll bet that sucker's gonna be bad to the bone when you're done. Looking forward to following this build.
I don't know about Challengers, but I've heard of Cudas built for CA that don't have cut outs in the rear valance. They just had turn downs. Something to do with emissions.