Info on upgrading Wheels and Tires

I would like to upgrade wheels & tires on a 1991 base vert to 18 x 9 1/2. Has anyone done this and if so any problems that I should be aware of. Considering 5 spoke C5 reproduction wheels.

Thanks in advance.

"Save the Wave" 

For awhile I ran a set of 18 x 9.5 C5 wheels front and rear on my 1994, no problems with clearance, ran 275/30 tires...the one thing different is the wheel offset...the C5 wheel has more offset and will tuck back in the wheelwell about 1/4 to 3/8 of an inch...not much, but I didn't like the look and bought some 1/4 inch aluminum wheel spacers to bring the wheel out to the edge of the wheelwell