Caster and vibrations

I am in the process of adjusting the caster on the XJ which I think is off. I have been experiancing shake at speeds between 55 and 70 mph for some time now and now is trying to do something about it. With the front drive shaft off, the vibes are gone. Late last year, I broke one of the brackets that attaches the lower control arm to the axel and made my own. Directional control is great, no obnormal tire wear and the XJ handles great.
My question is, can I check the caster on both ends of the axel in the drive way?
What would be the recomended caster for 1.5 inch lift?
TIA.

Does the shaking go away at higher speeds?

Recommended caster for 1.5" is around 7*. Or within factory specs.

Normally shaking between 50 and 60 MPH is caused by wheel balance. If it disappears when the front drive shaft is removed, it's obviously caused by the drive shaft -- why would you be playing with caster? Take the drive shaft to a shop and have it balanced.