Paul. I can't quote a source for the info. but I've always believed that the intake manifold gaskets with the small crossover hole were used on some Ford production 292 truck applications.
I suspect that the original Ford application was larger vehicle 292 trucks. -Not pick-up trucks.
I THINK their use by Ford originated in the early '60s.
Someone with a set of Ford Truck Text Catalogs can probably identify their year of first application.
Removing the exhaust system heat riser and using a Ford production spacer instead, OR removing the flapper valve but keeping the shaft, coupled with using the intake gaskets with the small hole in the heat cross-over, should reduce the engine's intake manifold temperature AND the operating temperature of the carburetor on the intake manifold.
Mac's shows both a reproduction exhaust manifold heat riser replacement spacer and an exhaust manifold heat riser with a stainless steel shaft that has no flapper installed if you look up '57 Ford exhaust system. Interestingly, I don't see a Mac's listing for the intake manifold gaskets with the small hole for the exhaust crossover.
Ebay has a listing for the intake manifold gaskets we're talking about from BEST Gasket. Click the link below.
http://www.ebay.com/itm/Ford-Edsel-Mercury-272-292-312-Y-Block-Intake-Manifold-Gasket-Set-BEST-1955-64/190905115430?_trkparms=aid%3D222007%26algo%3DSIM.MBE%26ao%3D2%26asc%3D46086%26meid%3D68eb72f09f0548ea919c5b11bd21b3e0%26pid%3D100005%26rk%3D2%26rkt%3D2%26mehot%3Dlo%26sd%3D222622085425&_trksid=p2047675.c100005.m1851Hope this helps.
NoShortcuts
a.k.a. Charlie Brown
near Syracuse, New York