Front backspacing is same as original, and will vary depending on what size wheel you decide to run.

Rear requires 1" LESS backspacing per wheel to make up the difference of having a 2" narrower rear end. (Or use a 1" adapter/spacer)

What size wheels are you using?

Front 17x7 is best fit with 235x45/17 and 4" backspacing.  You might be able to run an 8" with 4.5" backspacing and a 245x45/17 tire, but be sure you check all clearances for the fender lip.  You can roll the fender lip upward to be sure.  If you don't, it can catch the tire and cut it, and if that happens at speed, you have big time problems.

18x8 in rear, use 4.5" BS.  As a general rule, for every extra 1" width, add 1/2" backspacing.  This works up to a limit...   ( In your case, subtract 1" backspacing from these wheel dimensions since you have the narrower rear axle.)  Some have run wider rims in the rear, even up to 10" but they will have to chime in to report what tire and backspacing was used.  I am typically more conservative than teenagers on wheel and tire size, opting for something I do not have to worry about ever cutting a tire and causing a blowout.