Extreme clutch shudder

I would think the pinion would have to be 'yards' off to cause that. Is this a stock Mopar rear? Unless you have the springs all jacked around, should not be an issue. Have you measured the pinion angle?

Put the car on some sort of blocks so it's fairly level with weight on the suspension. Measure crankshaft centerline for angle. Measure pinion angle. The difference between the two If one is up the other down (from level) you'll have to make allowance for that

The "normal accepted" seems to be having the pinion about 2* down relative to the crank/ transmission

Regardless of pinion angle, you may have a suspension problem, bushings, loose shackles or U bolts or broken leafs. Don't discount that and check carefully.