REAR LENGTH

your leaf springs are what have to be moved first, then the wheel house has to be widened. then shorten the axle to suit the backspacing of the rims you want to use. you can adjust how the tire positions in the wheel house with different backspaced rims but you can't go larger on the tire if it wont fit in the wheel house or if it is too close to the leaf spring.

plenty of cars hooking hard and going fast on 8 inch slicks. unless your going for the "look" or street racing where traction is everything on a non prepped surface I'd just go with the 8's. lot of cars yanking the skinnies and running 10's on 8's. total width on an 8 inch slick is like 9-9.5 inches depending on rim width. all race tire manufacture's advertise this or will tell you the exact dimensions thru their tech line.