offset and rim size questions

So my dart has the sbp in back with 1 1/4 adapter plate to bbp and I want to order some rims. I have the bbp in front, no prob. Jegs has their sport lite with 5.5 back spacing, 15x8, and I want to know if this would fit with the spacer/adapter in the back of my 73 dart swinger!! I believe I have read that people run 8 inch rims in dart's with 4 1/2 inch back spacing, and I would end up with 4 1/4, no prob, right? This car is just a cruiser, I'm not racing anyone so I don't mind the adapters for now till I can afford the rear end I want, this will be fine. But if some one could tell me if they are running 8" rims please clue me as to spacing and tire sizes and you'll be helping me alot!!