I know nothing about a 250 ci engine, or its intake manifold.
Here is a quote from a Tom Langdon write-up that someone linked to years ago regarding a 250 intake's heat plate.
"Our heat plates are not sold with a gasket, but a gasket is definitely required. Use the gray color RTV or make a paper gasket and add gray RTV (ideal) or a factory type gasket with RTV."
