[60-66]

Heater controls : 3840038 is the number for 1964-1965 , it changed in 1966 to 3885187 for heater controls. Then in 1967 3885187 became 1964-1966 as GM grouped these together for "Service parts". Changes like color were not always well defined in parts books but the numbers are if you dig deeper. This IS the reason for Parts History books , to see when changes were made.

The AC Dash Bezel: 3840708 is the 1964-1965 Fawn bezel. Interestingly the DO list a different Production line Bezel as 1965 3866140 which is light fawn , seems as 1965 late AC was installed on the line . 1966 Dark Fawn AC Dash bezel is 3885191 and is specific number because it was cast in a different color.

The N.S.S. reference you see Tony , my guess is your using a much later print dated parts book. The older books show these numbers in the drawings also.

Air Conditioning Accessory kits : 1964 kit for 283 truck 985892 , 1965 986269 , 1966 986441.These are all "Basic Kit 283" accessory numbers , NONE of the part numbers overlap to other years. Each year had some small change or parts added or deleted. Theres a different "KIT" number for each engine also.

1966K10 , your dash bezel , my best guess , dealer installed something he had on the shelf OR your bezel was replaced some time in its life. Your AC could have been added AFTER your truck was bought new , like a year or two later. All are possibility's. Theres NO WAY of knowing that this bezel was installed in your truck when it was New without original owners adding that fact or tracing the trucks owner and service history. If you take your underdash unit off the firewall and out of the dash , there are inspection stickers that may give you a hint to the date of your kit but thats a long shot that thats still glued in place.