To run the HD sprag you will need a drum from the 60's to accept the new sprag. Also get a 4L80E intermediate palte and frictions that way you can run 4 clutches, and not 3. Use teflon scarf cut seals, I would reccomend replacing the bushings. Therre are tons of mods you can do. You will be fine with all the above listed in above postsbigdummy said:A laundry list of items you might want to throw at that tranny. I would recommend all of them, if you can.
-Trans cooler - for off road use, the bigger the better
-Deep oil pan
-34 element intermediate sprag clutch
(When I built my TH400, this was the ONLY internal upgrade that B&M said was necessary to hold up to about 570HP & 500 ft-lb of torque)
Also, if you ever turn more than about 4500 - 5000 rpm in 1st gear, you will need to get the appropriate valve body, or make the appropriate modifications to keep it from automatically upshifting to 2nd. Usually just a modification to the 1-2 shift valve.