Make them equal. Tranny 3* down, pinion 3* up.
Your rearend needs to come up 6*.
When setting up a new rearend don't tack the perches on until you have the rearend sitting at ride height on the ground. Set the pinion angle, tack it into place, remove and finish weld.
Here's a link on pinion angles.
Pinion angle? - The 1947 - Present Chevrolet & GMC Truck Message Board Network