I have run 228 carbs on 270's. No problem idling, no problem with throttle response, but I did give up top end power. I agree you should look for a 270 carburetor, but all of the problems you describe are not caused by the mismatch. I started driving a GMC with a 228 to school in 1958 and have been messing with GMC ever since.
Until you find a 270 carb, you might try revving her up and then holding your hand over the carb to cut off the air supply. Quite often you can suck the trash through the carb with the high vacuum.
