I'd suggest a 4340 torsional input shaft, a 4340 torsional intermediate shaft, a steel forward clutch hub, a direct drum with the 36 element sprag, the high lube modification, the improved snap ring, and the heat treated outer race, a four clutch intermediate pack, a roller thrust bearing in the rear of the case, a reverse pattern manual valve body (the only way to get a good brake), an Allison filter, and a deep 1 ton truck pan.
While the straight cut planetary sets offer reduced drag, and we used them in Stock and Super Stock eliminator cars, we've also experienced breakage. The torsional shafts are designed to drasticly reduce such failures, they work like the torsion bar cluster shaft in an old Doug Nash road race 5 speed. They twist and spring back to absorb shock.
If you are racing headsup and especially if you are running against a Pro tree, buy the Griner brake, it is simply the very best brake for a 400 there is. It's also about $200 higher than anything else. You'll ne a shield too. You are close to the level where you'll need an aftermarket center support and a different style second gear setup. If you are at 1000 horsepower and over 3000 pounds in weight, you're there already.
