Unless you've got the triangular brass tag with the part number stamped on it, you're sort of SOL. Casting numbers don't mean much on early Rochesters before they started stamping the part number on the float chamber castings. Various carbs with widely different calibrations used the same castings. The bigger throttle bore for the 261 carb makes sense.
Jerry


"It is better to be silent and be thought a fool than to speak and eliminate all doubt!" - Abraham Lincoln
Cringe and wail in fear, Eloi- - - - -we Morlocks are on the hunt!
There is nothing noble in being superior to your fellow man; true nobility is being superior to your former self. - Ernest Hemingway
Love your enemies and drive 'em nuts!