Do you mean before or after I move the springs with the offset shackle kit?
The Prostars in 15x8 only come in 0 offset which will put the backspacing at 4.5 or 25 offset which would put the backspacing at 5.5. So I think I should go with the 4.5 backspacing.
Did you see Longgone's cuda with the 275 tire without any mods?