Thanks for all the responses.
I bought these 6 lug wheels and Goodyear tires from Bandit Resins. Several people are selling them on ebay. Both wheels and tires are plastic but well made. Here is a photo of what I bought.
DSCF0004 (11) by
Nathan Pitts, on Flickr
The tires seem to be made really well. These are Goodyear. They were used on the Black Widow 57 Chevies and for a few years after. These are 7 1/2 inch wheels. They were superseded by the Holman and Moody 9 inch wheels in 1962 or so. The H&M wheels must have resolved the wheel breakage issues as they were 5 lug, on the Pontiac pattern. But everybody used them after that. I sand the treads up to make them look like they have been on a car, then mask the treads, and spray the rest of the tire with matte gloss.
I just had a hip replacement yesterday so am not moving real good at the moment. My bench is downstairs and it will be a few days before I can do that but will paint up the wheels and fix up the tires so I can see what they look like. The wheelbacks are made for steel axles but look like they have enough meat to be bored out to fit the 60 Chevy kit snap-on stubs OK.
I am glad I found someone who makes wheels and tires to fill that gap between street tires and full racing tires on H&M wheels. I would recommend these highly and they are not expensive at all for the quality.
MB