I was just looking at three different cams I have:
1. My original 1957 EDB with a #4 above it:
2. 1961 truck cam
3. A factory replacement cam which I believe from what I have read are like the 62-64 truck cams?
After doing some measurements the 57 EDB cam has a smaller base circle then the other two? Maybe there is something I don't know but I would have assumed the base circle would have been the same on all.