I've got a '78 CJ-5 with a T-150 and Dana 20. I've recently aquired a T-18 that I'm rebuilding and swapping in. I figure while I'm at it I may as well try to swap out the Dana 20 with a 300, but I'm concerned about the driveshaft length. How short can I go? My rear driveshaft is a custom made CV type that measures 18" in length. :usa:

I think 14 is about it with a CV but PM Onetoncv and Jess of High angle Driveline will tell you for sure.

In my 79 cj-5, I currently have a 304, t18, d20 and I run a 13.5" rear cv shaft. Works great.