All of the early napco conversions had a drivers side differential and used the rockwell 2 lever tcase (not spicer 24)
Sure you're not thinking of the Coleman 4x4 conversions? All the information I've seen on Napco trucks point to the Spicer 23/24 T-case as the one most used. However, the Colman did use a 2 lever T-case of their own manufacture (model 22 part time and model 42 full time, all gear drive) that does resemble the Rockwell.
Napco 4x4 is the best place I've seen to find information about Napco trucks of all kinds.
