I aquired a trail rig last year with some issues I am attempting to fix to get it out on the trail. The first one I am working on is the transmission/tcase/driveshaft interference issues. The powertrain in the Jeep is a 401 (fairly stock running on propane, Edelbrock manifold, headers, but I plan to get a cam that matches pane better!!), to a recently rebuilt TF727 with a BM converter, to a 4.1 D300, going to a narrowed D60 front (another part of the problem), and linked 14 bolt rear. After researching the cost of a 2 piece driveline, I found locally a 72k TF999 out of a 1994 YJ. I assume this will cure the driveshaft issues, what things internally can I do for a reasonable amount of money to help this thing live. I plan on a full manual reverse valve body with compression braking after some research on this forum about full power assaults and broken sprags, what else can I do?? I assume the torque converter will not swap over from the TF 727 because the 999 is lockup ? (again I think)

I run a TF999 behind a warm 360. Just slap a huge cooler on it and go. The thing that helps propane is compression, not a cam. When I finally get around to building my spare 360, it will be in the range of 11:1 or so to take advantage of the high octane rating of propane.

Do a HD rebuild with quality parts and rivet the rear sprag to the case. Don't get too stupid with the go pedal and it should live for a while.

my 999 is holding up very well behind my lt1. and im all over the skinny pedal.
im going on 3 years with only one annoyance. i need to slap it in nuetral for a few secs when warming up. otherwise it doesnt wanna go. but this is after it sits for awhile.
do the vent relocation and get the biggest cooler you can with a fan preferably and you should be fine.

ive got a 700r4 waiting to go in but my 999 just wont die.

DEEP PAN!!! Mine would always suck the pan dry on steep climbs. Also the TF does not circulate fluid when it is in park; but you can modify it to flow in park, or just leave it in neutral when it gets hot....

Deep pan, external cooler. I did both of those on my auto trans, and I love it.
Scott

Mines got about 7 years of senseless abuse on it behind a 5.9 with everything from street to comp driving and everything in between. Mines pretty well built, but for all intents and purposes a big cooler and a deep pan (if you can fit one, I can't) will go a long way and cost very little.