A couple additional comments -
a) I learned something new from this thread; I didn't realize those additional characters beyond the three space RPO code actually meant something. By they time I started in the '"73 and beyond" those had been reduced to mere dummy characters as placeholders. Now I see why they were there in the first place.
b) My professional expertise is in full size truck engineering and assembly, starting in 1979. My historical focus is the Pontiac Michigan assembly center of the mid 1960's.
If you have some time to do some general reading I would recommend these links:
This is specific to Camaros, but applies to all GM assembly plants in general
http://www.camaros.org/assemblyprocess.shtml#chev
This is more related to '73-'87, pictures with some insightful commentary:
http://www.73-87.com/7387info/Assembly%20Line.htm
The definitive overview of Pontiac passenger car assembly in the mid 60's ("Made in Pontiac" series; 5 parts):
http://wildaboutcarsonline.com/cgi-b...=9990401240631
This will give you a basic overview of how the cars/trucks were assembled, and therefore what the requirements were as far as receiving the RPO information, how that was disseminated through the plant to help facilitate the build, and how the parts needed to be configured to accomplish that.
I'll try to take some time and read through the previous 3 pages to see if I can learn something else or perhaps share some insights.
K