It's not GM, but my '68 Seagrave Fire truck has the Waukesha 817 Straight-six in it, and it sounds like a MONSTER. Of course, compared to Diesels, it's not so loud, but yeah, you hear it coming. These engines I think were born in the early 50s, as the 145GZB, same engine, different name. Two plugs per cylinder, dual ignition, dual batteries, oil cooler, governor . . . a beast.
Been around the Mack 707 a lot, too. Buddy had one with a knock, turned out to be a hole burned in a piston - wrong heat-range plugs, and plug was loose in the whole, let air in. Lean condition led to overheating. He ended up buying a whole other truck to part out, just to get the replacement piston he needed.
Rebuilding a 235 is a LOT cheaper! ;-)
-Michael
