Here's what I did when I redid the wheel in my 51. My local hardware store carries PC-7 epoxy. It comes in 2 cans for about $10.00. I first filed and cleaned out ALL the cracks and knicks I could find using files, a hacksaw, and a Dremel tool with various attachments. Make sure to take the cracks all the way down to the wire frame and V the cut if possible. You'd be surprised how big the cracks get since they seem to keep crumbling and getting larger as you go. I then mixed up the epoxy and filled the cracks. After each application I filed and sanded and some areas took 3 or 4 applications to get it right. Was very tedious, especially getting the reveal lines to look good. I used small wooden sticks, dowels popsicle sticks, etc, as sanding blocks. After sanding the entire wheel with 80 grit(go lightly as the rubbery base sands very easily)I primed with a couple coats of epoxy primer and sanded with about 120 grit. Another coat of epoxy and sanded with 240 grit. Another coat and sanded with 400. The epoxy sands tough, but I figured it would hold up better than a surfacer. Then finished it off with a couple of coats of single stage urethane I had mixed to match the steering column that still had nice original paint. I was real happy with the way it came out and other than paint, my only other cost was the $10 for the epoxy and a few sheets of sandpaper.
Forgot to add, before starting and at each step I cleaned the wheel with a wax and grease remover.
