Truck design should not vary much by gauge. It would just be a matter of changing the bolsters and axles. We often see older designs on the narrow gauge, because there was not any reason to replace them with more modern designs.
I'm not sure now many 42" gauge operations there were in the US when you exclude the several streetcar systems (LA, Cal., Denver, Col., Portland, Or.). But, in Canada there were 42" gauge operations on Prince Edward Island and in Newfoundland. Also in Central America there were several 42" gauge lines that used US technology.
Brian Norden