I have a '65 with 5" lowering springs.
Did you buy an adjustable panhard bar? If not than the rear axle is already pushed to the right. If you put an adjustable panhard bar in you can center the axle.
The axle moves about 3/4" during travel and full articulation. The following link (See post #17) has data I created that shows axle movement
http://67-72chevytrucks.com/vboard/showthread.php?t=430738&highlight=track+barI have about 1" clearance on on my truck but I like the look of having the tire close the the fender. Check out the link below to view a photo of my truck for ref. I hope this helps.
I don't know why this post was moved to the "The Hi-Po Shop" forum? It would be best if it were in the 60-66 forum. Thanks.