A few things to consider:
If you lose the torsion bars, you will have no rear support for your lower control arms. They will not stay in place without implementing some sort of lateral support to the rear. I have no idea how one would accomplish this, or at least no idea I consider worth suggesting (because of the hex-shaped sockets). This isn't an eventual issue, this is a "your control arm(s) will fall off on the test drive" issue.
On the coilovers, you'll have to fab new shock towers. The factory A-body ones are notorious for failure with virtually no load on them; put 55% of the weight on the car on 'em and they'll probably blow apart before the jack's fully unloaded.
If you're going to lose the inners, make sure any and all support structure that's going to replace them is in place prior to making Cut One in removing them. That means if you're going to use cage tubes to support the front end of the rails, they need to be welded to an installed cage first, meaning at least a six-point (though you wouldn't have to have the trunk braces in yet). Unitized construction is very complex in its load distribution, so make sure it's over-supported before removing anything. It will buckle with no engine in it--in fact, having the engine out won't make it any less likely to do so, unless you've already got coilovers in place. Remember, once the inners are gone the core support is of absolutely no use in terms of structure. Tying into it might strengthen the support itself, but will accomplish nothing for any other weaknesses in the car.
Make sure everything you do will pass an NHRA inspection, or it's likely they won't let you onto the track. In Atlanta, if it even looked like it would run faster than a 12.00, it got picked over with a fine-tooth comb, and the more cut up the car, the closer the inspection. Anything flip-front over a tube chassis stub needed to be certified. That was Atlanta, though, which is an NHRA track. Your local track(s) might see things differently.
I'm assuming that at this point you're not buying that '74 360 Challenger Rallye?