Back in 1970 or so I made wider wheels for my Spitfire by getting a pair of
Corvair wheels, having the hubs punched out. The center section of the
original Spitfire wheels was centered for correct offset and then welded
into the Corvair rim.
I have no idea what scrapyard steel rim would be available today with a
matching diameter to a spridget steel wheel center, but if anyone knows of a
possible match...? As I recall I ended up with a great pair of wide rear
rims for about $50 total. I had come by a pair of still useable racing
slicks that were great on the rims.