[jgpnashville]

That's exactly what I thought, but that's not consistent with everything I know about the truck. The first and only owner prior to me was my employer. The truck was bought in 1967 as a work truck and sat unused for the past 20+ years until I resurrected it this year. I have the original bill of sale with all the info from a long-defunct dealership here in Nashville. It lists the truck with "305E Motor, 4 speed trans, 4 Wheel Drive, etc" so the SM420 4-speed would appear to have been the transmission that GMC shipped it with, unless the dealer swapped transmissions prior to sale. That seems unlikely, but not beyond possibility. Perhaps the Protect-O-Plate is in error?

I know the truck cost $2,938.65 when new and was purchased on 13 Oct 1967, presumably as the last-of-stock on '67 model year, since the '68 models would have been out at that point.

Thanks for all the thoughts.