Couple of pointers based on the good advice from above...
Centering the axle (after lowering this is needed - with an adj panhard or watts link) is a cosmetic thing, to be sure, but an "offset axle" can
also lead to tire rub if you have some meaty rear rubber.
1. To center the axle on an S197 the car needs to be at ride height (this can be simulated on a lift with the rear springs removed and the axle compressed to ride height). Tape strings at the center of both real wheel arches, then hang a "plumb bob" from each, to make them drop straight down. That's the fender indicator for both sides. Now measure inboard from the strings to the sidewall or rim face on the rear tires. When these two numbers measure the same (at ride height), the axle is centered.
2. I think the previous poster meant to say "use a digital angle finder" (not protractor) when he explained how to measure pinion angle. Adjust your lower control arm lengths (and/or upper arm length, if you have an adjustable upper) to get the pinion angle you want. Ideally the angle of the transmission
output flange is the same (but
opposite) of the angle at the axle
input flange, at ride height. Usually it is about 2 or 3 degrees, from memory.
This "optional driveline angle" theory works for a 1-piece driveshaft, but gets a little muddy for the (OEM) 2-piece driveshafts a lot of modern cars have.
Cheers,