8 3/4" swap info
Difference at the yokes between a 7.25" rear and an 8 3/4 is 2.25". So if you changed from a 7.25 to an 8 3/4, changed nothing else, and the driveshaft was the right length before then taking 2.25" out of it should work.
Best bet would always be to measure. Measure twice cut once as they say.
Looks like an early A, so what exactly is the Demon measurement good for? Also, that's not the factory measurement for Demon with an 8 3/4.
The gentleman did not state what A body Wheelbase he had or what transmission.
I did not assume that in his picture was his car he was currently working on!
I measured my Demon just to give him a starting point of reference as I stated.
The 108 Wheelbase is the most common of any of the A bodies.
The rear ride height and spring configuration will also affect the length a bit.
In anything except a restoration that is completely production original = You
need to measure it with the car with weight on rear end.
The reason I asked what year it was = I own a dozen turnkey A bodies with
all different Wheelbase and transmission combo and I would measure any
one of those on a 4 post ramp and give him my measurement that would get
him close enough to double check his measurements against.
What is a reference point good for = I have often mismeasured things the
first time around AND I do not trust charts without verify them.
