According to this page,
https://gmcpauls.com/67-72_gmc.htm your truck is a 67, as it has a 14 digit VIN as opposed to the 13 digit VIN of 68 and 69. I have yet to find out where the VIN is stamped on the frame. You'll possibly have to research glider kits or rolling chassis production to find the location of the serial number on the frame. It ends with a "B", so you know it's in the 60001-10,000 GVW range. Find some vintage shop manuals and they'll probably give a location.
