Trans Considering doing a transmission swap on my CJ5

[Newt]

I recently finished a re gear on my 1976 CJ5 that I’ve been building for some light river crawling. After completion I decided to start changing fluids on the rest of the powertrain and I was greeted by my Transmission having at least a half gallon of water in it and no oil. I then decided to pull the Transmission and the t case to see how bad the damage was. Long story short they are both in need of a rebuild a the least. The Transmission is the T- AMC 150 3 speed mated to the Dana 20 t case. Im looking for some insight on possibly doing a Transmission swap. From my current research I have my eye on the T- 18 4speed but Im not sure which versions (jeep,ford,gm) would mate without much tweaking. Also if it would be a good idea to go ahead and also swap to the Dana 300 t case. And If the T-18 Dana 300 combo would even fit in my CJ5 .

Its an I6 AMC 258 i6 / 4.2l with 4.88 gears on 33s Dana 30 , AMC20

Any ideas, suggestions or information would be greatly appreciated.