First time I ever saw head to block spacers was at a drag boat race in Columbiaville, MI +/- 1980. They were about two inches thick on a Pontiac Ram Air V headed, blown alcohol boat lettered as "Fool's Way", along with similar crankcase "extensions" on the sides of the pan rails. I stared at that concoction for about an hour trying to understand what I was looking at. Never saw inside of it, but that sucker sounded like a nitro motor and owner the water beating out a ton of Boss 429 and BB Chevy powered stuff.