According to American Limited, what we are all generically calling a "Commonwealth" truck is actually based on an 8' 6" or 9' 0" wheelbase GSC "41-N" truck. There were many variations on this truck manufactured for cars between 1945 and 1951. And in that vein, there have been numerous versions of this same basic truck manufactured in N scale over the years (Arnold-Rapido, Micro-Trains, Minitrix, Model Power, Rivarossi, Rowa, Walthers, and American Ltd). As one might expect, some are higher quality than others (and yes, I'm talking to you, Model Power) -
MRC Wheel Diameter 0.203" (scale 33")
MRC wheelbase 0.636" (scale 8' 6")