The American Classic web site has an axle decoder, but it has not been working for sometime. I used to reference it a lot for the 3/4 and 1 ton 4.10 codes. I wrote down all the 4.10 codes one day to have for my file. They actually showed a 4.11 (not 4.10) HO52 available as early as 1964.
Year Code Ratio
1964 MA, MD 4.11 3/4 ton
1965 HW " " "
1966 JU " " "
1967 HW, JU " " "
1968 and after was listed as a 4.10 ratio.
I don't have a Chevrolet by the Numbers book, I think they are out of print. But I know Bill does and it sounds like Denny has one also. Can you guys confirm these codes and ratios for '64-'67?
