What year and take manifold and engine?
OK, the Edelbrock Performer should use the older style water neck, thermostat & gasket. This particular old style thermostat measures 2-31/64, just under 2-1/2 inches.
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ThanksOk, I thought it ya have been a stock intake and manifold, hole in a second.... BRB
You may have ether the later thermostat housing or later thermostat.
does your vintage air elbow use a chevy thermostat?
the recess is in the orange elbow you showed or in the manifold?
just hallucinating here
what would be nice is if there was a way to use a thermostat that shuts off the bypass like the magnums or the 361-413 Trucks/ motorhomes
Hint for max cool put a heater valve In the bypass