A T-18 holds 2½ quarts. I'm running 50wt motor oil in mine. This was recommended to me by a transmission builder. Normally these transmissions are used in heavy trucks where the stress on the gears requires the heavier gear lube. In light weight Jeeps, that is not the case. Using 50wt motor oil will make it shift easier, especially when its cold outside.
Beat it to fit, paint it to match!
Wheel, Wrench, Repeat.