[Supras] Rear end upgrade for MKII

[Sevan D]

Anyone know of a independent rear conversion that is fairly straight forward for a MKII supra ?
is Reg still around ?
I finally got my car done, and even at 12 psi it is screaming thru the gears, I have a TH-350 tranny in it, and I cross the 1/8th mile in 3rd gear at 6000 rpm.
Once I get it hooked up, and turn up the boost .....
I know that I need less gear, as I checked my codes and I have a 4.11 or 4.33 gear, I can't remember exactly, but I know it is in the low 4.00.
Anyway I know I can get a different factory gear/ mkII supra housing, but if I can I'd like to upgrade to something stronger.  Anyone ever swap a mkIV center into anything ? are the guys with the 900+ hp MKIV's using the factory rear in the 6 spd cars ?
any info would help

Thanks

Sevan