Hell, If I could find that I would ditch my current new GMC. lol
It's a custom! The closest GM ever got was the Burb and it was only a 3dr at that with 2drs on the pass side and one on the drivers. The trucks only came standard cab untill 73 or later.
They actually did a crew cab on these trucks for the forestry service and state vehicles, it wasn't as cool as yours though. it had 4 standard cab front doors on it. Looked kinda goofy