The GMC dash cluster is a circuit board, of sorts. The bulbs are housed in a socket, that turns into the back, to secure it and complete the lighting circuit...different than the Chevy dash light sockets of the same year.
You got me on that one.
I know the GMC's have some differences from the Chevy's and this may be another one of them.
I did my whole dash on my 64 and never came across anything that looked like that.
Looks more like one of the lights from a 67-72 dash.
