IMHO (once again)....detune the Hemi using its current internals except a new set of H beam rods. I would use the crank you have, possibly even the cam. Rings, bearings, small stuff replacement are a given since it will be apart. Rebuild the trans you have with OEM internals keeping it 18 spine and current shifter / shifter location. Small sheet metal repair if required in the tunnel area. Heck, I would leave the funky ladder bars....not seen every day.
Clean up and rebuild only what is needed of the cool ride you inherited..... and don't go crazy changing what your FIL built. Preserve the basic look, but make it safe, reliable as possible and functional. Be practical and forget about making a daily driver out of a purpose built race car. That would almost require a complete make-over, not to mention a deep wallet.
Most are excited about what the car is.
and always remember.....my posts are mostly for entertainment purposes. Your car, your $$$ ...your build. Thanks for sharing.