I don't remember for sure(I put the Napco stuff in 10 years ago) and I don't have my truck here right now to look at. I think it was something to do with the tranny outputs. The 3 speed has a splined shaft output to accept a slip joint on the driveshaft and the four speed output has a U-joint yoke? Something like that. Maybe I just assumed it wouldn't go and didn't look at it hard enough. I'm sure it can be done. With your long wheelbase you will have more room for any adapter you may have to make for the shaft between the tranny and transfer case. My truck is a short one and there is not much room between the tranny and the transfer case. Rear driveshaft angle is pretty severe also so I wouldn't want to move the case back any further.
