Are there space for 9" and 4,5" bs at the rear? At summit Racing they suggested 7-8x15 with 4" bs front and 4,5" bs rear.
Regards Kjartan
All four items are important. Tire size, wheel width, wheel diameter, and wheel back spacing are all factors.
You can fit larger/wider tires in the rear than you can the front. So if you want larger tires in the front than the rear you can do it. If you want all 4 tires and wheels to be the same size then you need to concentrate on what you can fit on the front and then the rear should be no problem.
I suggest you stick with recommendations from other BOSS 302 owners who are already running the tires and wheels they are suggesting. Their tires and wheels fit!
Tire and wheel recommendations from companies that have products to sell you my be well-meaning, but their job is to sell parts.