The New Venture is a good way to get an overdrive and still have a good low hole. It is doable where I would say putting putting an OD in a SM420 is impossible from a practical standpoint. However if you have a 50 model with the original engine, I would agree with John. I think you will be too underpowered to pull any kind of OD.
Rusted,
You are correct that a 3/4 ton had a closed drive shaft to the center bearing and open from there to the third member. However, that doesn't mean you can't use an open drive shaft all the way from the transmission to the rear end.
