...I finally found out the origins of my desk set. This set was offered in the Mack Shop catalog back in 1990-91 for the princely sum of $82.50 at the time (...that's $136 in today's Monopoly money, but that's another story...).
That the truck is facing in the opposite direction is most likely a preproduction change rather than something done later in life, there is no evidence of tampering with the felt bottom.
The name plate shown was a separate piece, left loose to be engraved and then mounted with double side tape.
Many thanks to the Mack museum curator for helping me identify this piece.