69 Barracuda Clutch Shake Help Needed.

Got a problem with my 69 Barracuda I'm trying to resolve. I think I'm on the right track but would just like some other opinions. Car specifics are:

69 Barracuda Formula S Fastback, All original 383 HP, 4 speed, 3.23 SG rear. Original cast bell housing.

Past history by 30 year previous owner, car was put on jack stands some years ago after smoking the clutch, so a new clutch was needed. I bought the car last October and at that time shakes at a dead stop take off only. Put in the new clutch last week. A street Mcleod with Borg and Beck pressure plate from Brewer's Performance. Resurfaced the flywheel. All seems good on the rack. Good motor/tranny mounts. No binding linkage. Car does fine down the road once you get it rolling. Will take off fine in 2nd gear and in reverse form a dead stop but still shakes like crazy at a dead stop from 1st gear, even easing out. Yesterday I set the cars mercy brake and let out on the clutch while in 4th gear. Car dies pretty quickly. Then put the car in 1st gear eased out the clutch and throttled the car. Car wants to raise up with the brake set. But as soon as you let the brake out and start moving at all it shakes. BTW. If you are rolling much at all in 1st gear and take off easy. It won't shake. I'm leaning toward bad leaf springs and/or pinion angle incorrect.

Has anyone ran into this condition with a stick car and bad pinion angle? Car runs, drives, rides very nice otherwise. Only shakes violently form a standing stop take off in 1st gear.

Any suggestions would be greatly appreciated. Thanks.