I like the way the hub cap adapters on this page were made but making a casting is not something I do every day.
http://pic5.piczo.com/Millpower-Race-Engineering/?g=45768718I finally came up with an inexpensive way to attach my hub caps. I started with some stock rally centers I found cheap on e-Bay. I removed the center part with a cut-off wheel and grinder. Then I drilled 3 evenly spaced holes 5/16" in from the outer edge and attached the clips with #10 machine screws, nuts and star washers. I salvaged the clips from some damaged wheels I had, but you can buy them from some of the venders for about $3 each.
http://web.etv.net/users/jmcneel/hc1.jpgYou could go with 4 or 6 clips as long as they are spaced evenly. Probably a good idea if you drive much on washboard gravel but 3 clips seem tight enough for my purposes. I then simply bolt the modified center to the rim with 5/16" cap screws.
http://web.etv.net/users/jmcneel/hc2.jpgThen snap on the hub cap.
http://web.etv.net/users/jmcneel/hc3.jpgJust the look I was going for.
http://web.etv.net/users/jmcneel/hc4.jpgI've kept the chrome to a minimum for a more subtle look, only adding a few select pieces like my license plate frame!
http://web.etv.net/users/jmcneel/hc5.jpghttp://web.etv.net/users/jmcneel/59.html