The Rochester 2 BBL used on the 265 and 283 engines was a very good carburetor. There was also a bigger bore model used on Pontiacs and a few other bigger-displacement engines. That one got adapted to 305 and 350 engines 20-something years later. The 305's had problems with it because of the large venturi size and had to have a very high float setting to avoid an off-idle stumble and a lean surge at part throttle. The small bore carb calibrated for a 265 should work pretty well on a 250, but only if the manifold is modified to accommodate the carb base. Using an adapter to mate the 2-BBL to the one-hole original carb flange would be worse than useless.
Jerry

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