I am running 10" wide wheels with 255/50/17's on a challenger and have minimal clearance on the drivers side and 1/2 inch clearance on the passenger side. I have brought in the wheel lip a little, but prefer not to go more. Are there any options for shifting the axle slightly or do I just need to go with a smaller tire or different back spacing?

eyeball the 4 corner shackle to body mounts & see if there's room to move/slot em slightly

I had to put a 1/4 inch spacer between the wheel and brake drum on the passenger side of my 72 Challenger to keep the tire from rubbing the spring. Maybe it's a factory offset but 1/2 " what would that help ??????????????????????

Installing a 68-70 B body rear axle will give you the room you need, they are narrorow, and it is a bolt in swap.

My Charger had the rear offset to one side about 3/8" when I got it.
The front spring hangers were both installed to slightly offset one way, I flipped one of the hangers and now the diff is centered. Might be worth looking at?

Not sure what you mean by "brought the lip in"...Anyhow if all else fails you could cut the perches off and center the rear...And correct any geometry problems in the process...