You caused me to pull out my original Lionel Service Binders and sure enough, they only cover the 1947 671 and do not show some of the 46 specific details. Same goes for the K-Line and Greenberg collection. The '46 726 is very similar, and Olsen's actually went through and took the ' 46 726 instruction sheet and updated it to be applicable for the '46 671. I can't vouch for it's accuracy to be 10000000%, but it looks like a respectable effort.
I haven't uncovered anywhere where Lionel lists the explicit wheel gauge out side this generality:
Hope this gets you on the right track.