setting the pinion angle

I ordered the axle brace from Mancini today and also ordered some new perches. I had planned on re doing the perches for a while now because I wanted to slide the axla back 1/2 inch for clearance. I want to make sure my thinking is correct on the pinion angle. I need 2 to 4 degree's down in relationship with the driveshaft, Correct?

Yes 2 to 4 down is good. You should really consider the Dana rear. I'm not sure the 8 3/4 will ever live with your car. They are massively strong and look cool too!