[Paul Ceasrine]

Bill,
Yes, any decent machinist with a Bridgeport "J" head milling machine could fabricate an angled-carb-adapter. But,,,back in late 66', 67'/68'/69'
just plain old 273 street cars and 318 2-barrel owners grabbed those
"Marine Application" manifolds because they had the Holley 650cfm
already mounted on them. It probably looked nice, an easy bolt-on.
Until, they found out that at idle the carb would load-up. Most inexperienced guys thought the carb was messed up, and required a re-build or adjustment. Any experienced 273 owner could tell the difference, just by looking at the intake. I think just seeing a Holley carb mounted on that intake made them excited. The early 66' marine intakes are the ones, center shut-out area removed and level mounting base. Later in 66', the angle carb-mount came into play for the marine applications.
Simply put, anyone with a little knowledge would simply take a stock
273 4-barrel intake and cut-out the center shut-out area, polish the edges, and bolt-on a carb-adapter or heat-riser. Good for another
5 Horsepower at 6000rpm.
Paul