Carl is correct about 6 cyl and 4 sp in factory Chevy Napco trucks. Bill, I misspoke about T221. Thanks for the correction, always welcome. A Rockwell transfer, I think ,was a one year only in 1955. The 55.2 Napco used a 3/4T drivetrain.(more or less). Spicer not ready until 1956. Dealers installed Napco in V8's and GMC's were available from factory in a V8. I don't think there was "Factory Only" until 1960. If there was no prohibition about dealers installing in a V8, the "6 cyl only" may have had a different reason than strength. Production line issue? One RPO? (different length/parts from tranny to diff?), better torque motor? Exhaust pipe issues? Utility Co.'s, municipal, and rescue only wanted 6 cyl?
Interesting note:
Napco Owners Group Website.
"DANA through it's subsidiary SPICER had been a major parts supplier for NAPCO. They used SPICER Model 23 Transfer Cases for most of the GM conversions, procuring the units from SPICER's Toledo manufacturing facility. In addition, Rockwell Transfer Cases were sometimes used, and GM provided the majority of the other parts for the conversion, including the basic corporate front axle housings. Additional components included Hotchkiss driving axles and Rzeppa constant velocity joints."
It's not a T221 used in 55.2.
Here is bolter Frank VanderBroek (stranger) explaining his 55.2 Napco.
"Mater's Cousin has the rare driver's side pumpkin, twin stick, Rockwell case. In 1956 General Motors changed to the Spicer case, single stick, with passenger side pumpkin."
