Strange S60 Rear End Help

Thanks to all of you. I've had a number of racers at the track tell me to have the perches welded at 4 degrees down, the same basic info that GTX John suggested, then be prepared to use the shims to fine tune the pinion angle. I'm bracket racing as a retirement hobby, and only running in the mid 10's. If anyone thinks this is a mistake, please let me know. On Tuesday, I'll have Dr. Diff give me the final answer, and place the order. Thanks again.