So, you're talking about the add on overdrive unit?
I'd guess that would be a mutha to quick shift up and down to get 6 forward gears and two reverse.
Now the question remains will the tranny hold up to 800 HP.
mousepower, get the thing built right or buy one that will handle the big TQ and HP. Add on units are for RV towing in a dually or Motorhome for towing.
Yeah, some use them for deep geared units to lower rpms for mileage.Not a choice for big HP.
The tranny problem is an easy fix to resolve your question.
Thanks Pat for bringing ichicheck's idea forward, I was pushing a point to help the poster's problem without going out to left field and add headaches to the simple solution.