Dana 20 t case has the same bolt pattern as a Dana 18 and scout dana 300 case.
D20 is a very good strong t case, but lacks low enough ratio in low range.

The trans you have (provided it is out of a later model CJ) will work with a Jeep dana 300, but not your d20.

The biggest problem is that the T150 tranny you have is stronger than the 5 speed (t-5) anyday. so...the best solution for reliabe strong upgrading is to go with a t-18 4 speed, and keep your d 20 case or really upgrade and do a t 18 with a d300 behind that. Call Mitch at RMH Transmissions 303-808-1268 he can fix you up.

SD