I have had the same problem with a 51, there are a couple of years that don't have rebuild kits. The splines are the same, I believe, as for other years. My solution was to get a rebuild kit for a later year, and graft (mig weld) the spline onto my regulator. Why there are so many different regulators, I have no idea. It may be best to disassemble the regulator so that any plastic bits etc inside it don't get destroyed by the heat.
David
