Bubba327

I have an old Carter AFB # 3721 SB that I understand if made for the 1964-65 Chevy Corvette with the 327 engine with 300 h.p. I am trying to find out what the M4 on the bottom of the carb. means & possibly its value. The connection bolt on the automatic chock is broken off, so I know that will devalue it somewhat. I am trying to sell it for a friend who is fighting cancer & could use the money. Would Hemmings be the best place to sell it? Thanks for any help you can give me.