Re: Muncie M-21 in place of a T-176 4 speed on CJ5
There is no real advantage to this swap. Advanced adapters used to sell adapters for the car transmissions to the dana 20 transfer cases, I see these at the swap meets all the time no one can unload them anymore. For a 258 the T-176 is a good transmission. If you have money to burn, do it right the first time and do the granny low ford T-18 swap, or if you have tons of money to burn then go for a NV4500.
good luck, jjc