I have had great success using the heat blocking paste when I heat the tail end of the tang to put custombends into it. I forget whether the tube I have is "Thermo-trap" or "bloc-it" but I am sure there are several good options. I have heated the tail red hot with a generous amount of heat blocking paste applied and for good measure I ice the blade before and after.
I think a lot of old Wade and Butcher razors (especially those WONDERFUL moster sized blades) have the oversized oblong hole in the tang, makes me wonder whether it is wear or done on purpose. The last one I rescaled I used a piece of copper tubing from the hobby store as a bushing. Get it as close to the size needed to fill the hole, cut it a bit longer than the thickness of the tang, slip it in then flare the ends using one of those cheap little screwdrivers (like eyeglass screwdrivers). The light flaring holds the tube in place thne if you want you can sand the excess OR finish flatteing it against the tang. Use little brass washers between the tang and scales and pin as usual.