Richard, I didn't see your thread earlier or would have replied.....
I had Marsh build a set of wheels and they are 8 inches wide. I am running the same 38.5 Swamper TSL's you saw on it back in the summer. The flat on the way to your place inspired me to ditch the tubes!
They work just fine and the backspacing in 4.5 inches on these wheels so it gives it a wider stance. They also were very reasonable for custom built wheels at $96 each. Wheels to fit a standard bolt pattern may be even cheaper, and the 8 lug Chevy is so common. I'd think 10" would be a bit much for those tires and put more of the sidewall out there in the open.
"Free advice is worth what you pay for it."™