Back when I did a lot of tractor pulling, my Dad had some custom wheels made so that we could use 12" tires on 6 lug hubs; I don't remember what they where for but we ended up with these somehow. They are supposed to go over the center part, but they are a hundredth to small.
I was going to use them to make some spacers so I could get a little wider stance, but I found a problem. Even if they did fit over the center, I would not have near enough room between the lug bolt to weld a pipe in as the spacer, and still have room for the bolt and socket.
I think that instead of messing around with the center hole and tight clearances, I will just remove the lip in the center of the hub. This way, I do not have to cut out the large center hole, which will give me a lot of room for the pipe in the middle, and I will have no problem clearing the lug bolts.