8.75 Not centered?!?!

Hang on boyz
This won't work without the spacer installed and the endplay set. Currently there is no way of telling which axle will end up where. That's why it's best to not have the perches installed until the very last.
Unless you're using Green bearings, then just put me on ignore.
On the inside edges if you have 1/8 from the sidewall to the spring with weight on the tires, then you have enough room. To the inner tub-walls you need a minimum of 1/4 inch for straight line work, and at least 3/8 for bombing around town. I usually narrow the rear a little too much and then pound in the offending areas.
To the outside 1/2 inch is good at the fender lip.
Almost nobody ever sees both sides at the same time unless the car is on a hoist. And almost nobody can remember 3/8inch difference when wandering around the car. And it won't affect the handling. If it bothers you, install a spacer on the one side to even it up.
I prefer Timkins cuz I can move the axles around with spacer thickness and fabricated backing plate shims, as may be required.
I don't like the Greens; just personal preference. Timkins last forever.