Yes, Hole in the middle is 1 1/16" (27mm or thereabouts). 276 carb has a remote float chamber, despised by many. A later Monobloc carb will fit on a Plunger bike no problem, except it's a tight squeeze against the frame top rail on an A10. A7 with the lower block height is a breeze. Folks fit a later type carb in the belief that it is better. A well set up 276 is fine, and don't suffer seized throttle stop screws, common with old monoblocs. Do not neglect to fit a carb drip shield. Drippy drip and sparky spark are an unbeatable combination.
Swarfy.