It has been an interesting discussion to me on the logger versions. One thing I did find in one of my A parts books was that Cletrac offered a "kit" to convert a regular tractor to a "logger". Also I did see that model B loggers have 5 lower track rollers per side compared to 4 on a normal model B and of course there are more links (pads) in each track. I will try to copy that information and send it to Blake next week and he can add it to this site.
My 1945 price list doesn't list any kind of B or D as a "Logger". All it has are the A and FDL and FDLC.