Anyone know if there were any significant differences in a 90 vs 91 small-block 518? Or how much it takes to swap a tailhousing for a transfer case?

 

The 518 in your truck should interchange with the one you are looking at as far as the year. You should know that a trans from a diesel is different than from a gas truck. As for the tail housing I honestly do not know. Some one else will have to answer that one.

 

I have a half ton that needs a transmission and found a junkyard with a 91 while looking for a Ford 302 to 4-speed-w/granny-low-gear bellhousing last night. I would imagine that they should swap right out, other than the yunkyard one is 2 wheel drive.