My thought is that GM found over time that a FOUR point system was superior. So anything after 1948 was a 4 point mounting system. I have a 48 cab and the plan is to get all the mounting parts to change it over to a 4 point system. Of course if you are going stock only, that is excluded. You can find cabs in salvage yards with all the parts you need, or go with new vendor parts. Good luck!
