Bax, you are wrong. I purchased a stack from tower a month or so back that was listed in teh 56 parts and I installed it on my O.S. 52 Carb, which has the same part number for the body. They are both "N" carbs. The 56 version in addition to the stack has a different barrel which changes the mix ratio in the mid range some. I haven't seen the parts list for the 81 yet, but I'm betting money that the same situation exist there where the carb is based on the 70's carb.

Don