Older Chevy/GMC wheels were 16x6", then they went to 16x6.5". Older Ford/Dodge wheels were 16x7". The only stock GM type of wheel that's actually wide would be the ones below, but they're 16.5x9.75", 12" wide from lip to lip. There was also a 16.5x8.25" wheel made but I've never come across one. I have two of the 9.75's on the back of my C20, and two for my Suburban sitting in the garage. I'm picking up two more Thursday so I'll have a set of four.
You can also send the 16" wheels to Stockton Wheel and they can widen 'em, not sure how much $$$ it costs but it's probably not cheap.
www.stocktonwheel.com