Guys, sorry it took me so long to reply to some of these - I have been doing extensive rework on my radiator core support. Now that it is done I will be putting the engine and transmission into the truck for final measurements. So far I know the NV3500 is 7 inches longer than a TH350 from the mount so I am estimating that the crossmember will have to come back that far. Thanks for the info about the height using an automatic crossmember. I think I will make my own crossmember so I can set the output degrees to zero like it should be. I haven't even looked at the driveshaft yet so I don't know what kind of work I will have to do there.
As far as I was told, the NV3500 was in full size pickups and S10s with a 4.3L from 1992 to 1998. The NV4500 is a 4WD transmission. Here is a link if you want more info on it.
http://www.nv4500.com/