the 250's will fit a 292 block but:
the 292's have a bigger propeller to pump more water. the 292 has a different type operation in that it has a bypass short hose up to the thermostat housing. the 292 pump bypass is there to keep steam pockets from building up in the head and it keeps the water temperature more even to keep the cylinder wear even between front and back. it is a true truck motor and designed for the most part not to overheat.
250
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292
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