My brother and I are Hellcat swapping his 71 Demon

From a former Pinellas County native, Welcome!

We have a great modern swap forum here. The rabbit hole goes deep. You can get lost for days reading through the posts.

My suggestion would be to get the full plug and play harness to make the wiring a little easier. It's not exactly cheap, but simplifies the process. Also, you may have to modify (or BFH) the tunnel to fit that transmission.