Well, Bill. Thank you. That establishes what was printed in 1957. And, it clarifies that the
part number that is shown at the top of this page came from the manual and was combined
with this image. Thank you for confirming this.
And, that almost answers your question:
"question: when did the term "RPO" start? the RPO numbers are actually the part numbers of the item". The item being an accessory (in this case).
In 1957, your documentation shows that the acronym "RPO" was used with accessories, and the actual part number of the accessory was used as the suffix.
That was not the case for Chevrolet truck accessories through at least 1954. The acronym "RPO" was not used for accessories; however, the part number was used to ID/order the accessories. I do not have an Accessory Installation Manual after 1954, so I do not know when the terminology RPO+part-number started to be used.
Here is how the part numbers are listed for accessories in 1955/55-1st. And, here is an
example of an instruction-page.
Do you have an accessories price list for 1957?
Here is how accessory part numbers are listed in the 1954 price list. Through at least 1956 and in 1960 (the years for which I have USA Truck Data books), RPO was used for Regular Production Options (factory installed options) and the number was the RPO number, not the part number.
Back to the heaters, the accessory Chevrolet Truck heaters for the two years after the Advance-Design years, were distinctly different from the heaters sold by GM for Advance-Design trucks. Here is a scan for
1955 and 1956 truck heaters (sorry, but I do not have the part numbers). A link to illustrations of 1954 heaters is in a post above. The 1947 USA Truck Data Book has
another style of heater that was not available in later A-D years, but it does not look like the heater you link-to above. Here is the
accessory heater page from the 1954 General Motors of Canada Chevrolet Truck Sales Data Book. The heater on the top looks a lot like the heater you show.
