The gasket in your photo looks like a ’59 and later 313065 gasket which has been slightly modified by being slotted on the left side. These gaskets for thermostat motors have a hole in them for the cooling water and aren’t open in this area like the ’56 – ’58 304314 gaskets are. I really don’t think it makes much difference which gasket you use as the water seems to find its way thru here easily. The hole might have been meant to be a restrictor to help keep the motor at a certain temperature, but I’m not sure. Even one BRP 313065 gasket I bought sure looks a lot like a 304314 gasket, and that’s in a sealed package!
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