Jim,I not running 18" wheels, but I am running 16" x 7". My wheels are acutally 2002 Ford Explorer truck wheels. I believe the back spacing is 4". These rims with 225/60/R16 tires on the back and 205/60/R16's on the front fit perfect. My 56 Victoria is lowered 4 1/2" in front and 2 1/2" in back. I have no problem with clearance I can fit a flat hand between the quarter panel and the sidewall. I can do the same on the inside of the wheel well. You can see pictures of the wheels in my profile or in pic's taken at previous year Expos. As far as large wheels go, it's all in your perception. I don't like "rubber band" tires myself and prefer some sidewall. But I have seen several 50's cars with 18's that look great. 20"s on the other hand is a different story!
Rob 