The problem is, when you lower these babies the driveshaft angle rises towards the rear of the car if you try to run equal and opposite angles with factory driveline angles(3-4degrees) the working angles reach 6.5-7 degrees or more. They can be equal and opposite but it will still cause a high speed vibration of some sort. I'd shoot for getting your driveshaft pointing down towards the rear of the car around 1 degree with a driveline and pinion angle of approx 2 degrees(equal but opposite. That will give you a working angle of only 1 degree and will run silky smooth until the car runs into the aerodynamic wall. (These are just estimates) Of course your rear suspension will effect if you need to put any preload in the pinion. With anything but leaf springs, I'd prefer smooth driving and less than ideal angle under WOT. Solid motor and body mounts will only compound any driveline angle issues and harmonic problems. I've done a little research and chasing my tail, can you tell.
