No longer rebuild carbs, but used to do lots of Q-Jets. Cannot remember even one where the epoxy on the well plugs was still intact when I disassembled the carb. ALL HAD FAILED!!!!! The epoxy would shrink slightly, and pull away from the edge of the casting. Often, would find the complete blob of epoxy totally separated from the casting in the bottom of the cavity. Rochester offered a foam spacer that would keep pressure on the epoxy, and keep it in place a little longer. All of these issues disappeared in 1968 with the revision to the method of sealing the wells to the 1968 and newer Q-Jets. The 1968 and newer don't leak, with or without epoxy. The 1965 ~ 1967 eventually leaked with every epoxy I ever tried, including JB Weld, and every other similar product available at the FLAPS. The solution to the leakage on the earlier Q-Jets was to remove the pressed-in plugs, and carefully thread the casting for screw-in plugs. There is a learning curve to prevent splitting the housing. Suggest NOT trying this on an extremely rare/expensive carburetor as your first attempt. Learn on junk before doing it for real. To the OP - I don't have an answer to what epoxy will work, I never found one; but if a 1968 or newer, don't even bother, it isn't necessary. Jon.