Here is a link to my previous post on the CC3 single wall top release information dated 01/72, for anyone that missed it.
http://67-72chevytrucks.com/vboard/s...&postcount=230
Since it was a supplemental release, survey of actual installations is an excellent idea. Based on the GM information single wall tops are expected on some mid to late 72MY units and I would be very suspect of earlier 72MY and down units.