Listen to DSE. A lowered pro touring Camaro requires the pinion down due to the driveline angle. My motor/trans is down 2.2, driveline down 1.8. I'd start with 2* down on the pinion and drive it and see what the harmonic are like.
Your key unknown is the driveshaft angle which determines working angles.
I'm assuming you're running a T56, what are the overdrive ratios?
If you have vibes - Make a note of or what gear and what rpms they occur at. Also note if the vibes are noticeable during slight decel & accel throttle input.
Be thankful you've got links to adjust vs leaf springs.
