A friend of mine in Europe has a 51 GMC with a 3 speed with worn synchros. His synchro is the one with the 2 lugs on it. I have several with the later 4 lugs. It seems to me that two of the lugs can be ground off and make the later ones work. I also remember updating some earlier transmissions 50 years ago, but I don't remember what all had to be replaced to go to the 4 lug synchdro. Has anyone worked on a pre 53 3 speed lately. I think they all had worn out synchros if they had any miles at all.