7" shouldnt be a problem with the right offset (I run 6.5" no worries)... but I dont think 8" would fit in the rear... Get out a measuring tape and have a look ;p
25 pos through to 0 offset for the 7inch wheel (factory example is the 14x7 8pos offset Supra rims).
The 8's will need a little more thought to make sure you don't scrub. However I have safely run 16x7.5's with 30pos offset on the rear around a race track with no rubbing.