Dave,

The 727 is the easiest, if you want overdrive without worry of blowing the thing up I would say 4l80E.

As far as the Mopar Nag-1 and 8 speed transmissions, They are much more work.

I believe hotwire sells a Nag controller but you still have to put sensors, tone rings, etc on the driveline. Way to much hassle in my opinion.

The Hellcat plug and play kit is for the engine only, it will not control a transmission.

Hope this helps