I think the confusion is over the double arrows. B + C is 35 inches, even though B has its own arrow. B is somewhere between 29-1/2 and 30 inches with C of course making up the difference.
As a somewhat related bit of info, the Squadron pub, GMC CCKW 2 1/2 ton truck, explains how it could fit into a C-47 thru the cargo door on pages 48-55.