Hi Dave,
For smooth wheel covers, you have to have the mechanically fastened. I.E. mine have been coming loose and falling off -- the spring steel grips are not adequate. I got them from Hubcap Mike, and they do also sell a screw-on style. They look great, but they require drilling and taping
through the rim:
Screw-On Racing Disc Wheel Cover Installation Instructions
I'm thinking that "coupe" style aluminum pizza pans would be better, and do something like tack weld nuts onto the rim?