Just finished my 4th season of autocrossing and all 4 were in my SRT6. The conclusion I've come to is, the most important mods are tires designed for autocrossing, negative camber and as much seat time as possible.
Our cars push in corners and I've found that lowering the rear air pressure 4 or 5 lbs below what you have up front will help. And again, negative camber comes into play here a bunch. Unless you've got money to burn, I'd recommend waiting on the pully and spending the money on tires and camber. The pully will help getting out of a corner faster but you've already got more power than you can currently put down.

Apologies if you already know all this.