How did Aquaman miss this one? He's got a nose for old and rusty.
A full size bus with a rear mounted gas engine. Belts running off of a pulley coming out of the transmission. In line six cylinder with an up draft carburetor. I'll bet it got at least 2 MPG if the points were set right.
No need to get dirty, stay out of the bus, you don't even need to poke around the engine. I can see the cache while standing up straight and not touching anything.