I'm not sure on if the T-case makes a difference, but I recall there being a change in the engine cross memebers at one point. It might be 78' and newer had a beefier cross member, which could effect the mounts. Another thing, there are different engine mount brackets between 4wd and 2wd but I'm not sure how to tell the difference. Might be worth your time to check out www.ramchargercentral.com. There's way more info there.

Mike