It can't be bolted up due to an integrated bell housing. You'll have to go with a later model tranny (post 83). As for the fifth gear, I'm running 31's on my 82 with 4.11 gears, and no fifth gear. By the time I get up to 65mph, it feels like I'm higher in the RPMs than I should be, and I don't have another gear to get into. I'm buying a rebuilt L50 five speed locally which will kill two birds with one stone.
do you have a tach?? i'm guessing not, get a aftermarket tachometer, not much $ and tells you what your engine is doing, a stock 22R is supposed to shift at 3600 rpm, which is where i used to drive on the interstate where ever i went when i had a 4 speed.
i never shift to 5th unless i'm over 65 mph