1972 Dart Magnum swap, R46RE Trans

Hello,
I already have a paper copy of the factory service manual and 40+ years as a Chrysler service technician.
We have narrowed the 9.25 diff and Moser built us a pair of axles so we can continue to run the 5 on 4 stock wheels..
the gears are 3.9 and Posi. (we may have to change)
120 Km/h is the normal speed on the side roads.. Car has to go 200+ Km/h !! or we get passed by a VW Passat...
Greetz, Bob