T18 T19 and 435 are all brothers. They all need the adapter! He already had a T18 so he was able to use what he had!
The T19 in the 4-1 and 5-1 synchro first allows you to down shift to first while moving. I had a T19 I put in a trail rig (74 cj5) and loved the ability to grab a lower gear while moving down the trail!
I trail road and wasn't rock crawling, so any lower first would have been un-usable for me but everyone needs to set the jeep up the best for them!
1984 CJ7, 258..HEI..MC2100, T176/D300, D30/M20 lockers, lift, warn winch!
"When in doubt! Gas it out!"