Help me identify some wheels
 

I need some help in identifying a set of 15x8 six lug steel wheels I bought for a 1966 c10 truck. I first thing I noticed was that the center was riveted in instead of welded. I know that normally means pre mid 50's. The second thing is they don't have the outside bosses or ears for a dog dish style center cap, nor do they have any holes or grind marks for the inside clips. The only identification marks I could find is 15x8, and a number 0 stamped on the inside of the band. There is also a circle about the size of a dime with 2 hash marks and a number 8 stamped on them. I would love to find out if they are originals, and if so what they came off of. If they are originals is a 15x6 available? Any info would be great.
Thanks