M6 Bomb Service Truck information.

[maple_leaf_eh]

I have no definitive information to bring to the conversation, however I've had two coffees this morning and am feeling a little brave.

I like your supposition that the individual seats could have been M6 Bomb truck parts. But .... notice the left side view at the link. The seat seems lower and the riser smooth-sided.
https://radionerds.com/index.php/Bom..._M6_(Chevrolet). There are other detailed photos in this 1942-dated manual https://radionerds.com/images/7/7e/T...E_TRUCK_M6.pdf

But, have you established (if it is possible) where and when your truck was manufactured, versus the M6 Bomb Truck's production history? You might be worrying about an impossibility. Yes Detroit is a small area, but the plants were flat out busy, and might not have cared to divert parts from their well-configured flow and process charts.