The T177 is the truck version of the T176. Yes you could have a T177 but it wouldn't be from a CJ because it has a long input shaft! The truck has a spacer between the bellhousing and the trany. With this added length, they are able to swap from auto's to sticks without changing drivelines or cross member locations.
The T177 has a lower first gear! No short inputs are available but you could use one in a CJ.
A T176/177 is a Ford transmission. If you went to a Ford 302 or 351, You could use the Ford bell housing and it will bolt up to the Tremec T176/177 transmission. You would need a adapter for a Chev conversion. I am a believer in the 4.3 Chev V6 but if you can find a 5.0 Fuel injected cheeper in a lot of areas.
A Buick V6 225 is also going to require a adapter unless you find a T18 setup but then you will find it with a D20 transfer. Keep the D300!
If you are willing to go with a $500.00 dollar adapter. Then A Chev engine and a Chev truck 4 speed would be the way to go and buy a adapter to keep your D300 transfercase!
AMC engines are heavy, costly to build and repair and although there are good EFI kits you can get! By the time you purchase a Howell EFI you can swap in a Ford or Chev engine and get more for your money!
I have run many AMC and Buick engines. And have a 258 in my current 84 CJ7 that I am waiting to go TU.
Novak is full of lots of info! If you have time and patience to dig threw!