Try looking at 65 impala, brake light socket. They appear to look correct. And do not list as 4020. Are your sockets metal or plastic?
pontiax- (canadian pontiac X frame)1964 Parisienne 2dr. Hardtop ,lagoon aqua metallic (Q) ,421 cid Dart Industries block and heads. 550 hp. 575 ft lb of torque.
They are plastic,I will give those a try