How do we blend race car and comfort?
OK:
1. I'd do a modern Hemi and the automatic transmission they come with. Up to you whether you use a supercharger.
2. If money was no object, I would go with a full frame that goes underneath your car. There are a few available. Here is one:
1970–1974 E-Body, Challenger, Cuda Chassis - Schwartz Performance
3. I would keep it looking as Mopar as possible on the inside. I'd find some really comfortable front buckets from a Lexus, modern Challenger, whatever. and have them re-covered to look as much like the original coverings as possible in leather. Have the rear seat matched.
4. Paint it a color available in 1970 with a hemi stripes.
5. Run the AC through Factory looking vents.