Back in the day when JD Dealers had their annual winter time "John Deere Days" with movies, prizes, and new product announcements, a GM box truck was used to carry the JD Days supplies. The truck became part of the show. It was using the 466 engine, but described as purely experimental.

I'm guessing this was in the late '70s.

By the way, most people I know miss the "John Deere Days". Their programs were always great. Great get-togethers at local dealers. It was a real pain for dealers though pulling employees to get ready for the show and having to move equipment to make room for the crowd. But still, most can remember just about every show they attended, though it was 50 yrs ago or more in many cases.