Those most definitely will not stick out on a Z31.
Check out Z31performance.com for moar info.
here's a couple examples of Z31's with 7" wide 0ET wheels:
not the best pictures, but they show that they most DEFINITELY do not stick out at ALL.
just another note, guys run 16x8" 0 offset ALL the time on Z31's, and they even run balloon tires with no probs