I had the same problem with replacement headlights having the prongs be too short to fit the socket. I was replacing the light because the prongs had broken off the light. I re-soldered the prongs and used the old light.

I saw the relay system discussed in a car mag and it sounded like a great idea. It's good to hear some of you have done it and it works. The relay system probably has new sockets that fit modern headlights. I may do this in the near future. I have trouble seeing through the old windshield with dim lights with my 51 year old eyeballs.