The issue is that the Balmar foot and the supplied bracket are not a close fit, and compressing the bracket across the foot will result in the casting failing, causing you a lot of pain if you are at sea, and costing a lot of money to replace it. Shims need to be inserted to pack out the width of the Balmar foot and reduce the compression on the bracket.
The above is from personal experience but clearly several others have experienced the same problem and neither Balmar nor Westerbeke provide any warning about likely failure.
While on the topic of Balmar alternators, I have asked this question before but now have more information, that of dusting alternator belts leaving black rubber dust over alternator and front of engine. I have had my mechanic check alignment, belt tension, free movement of alternator unloaded, and all are OK, but a brand new Davco TopCog belt still dusts and that is a belt recommended by Balmar.
The mechanic's suggestion was that the off-the-shelf belts are too soft a compound and that I should just get an original Westerbeke belt. I now have that and it is a much harder compound - haven't yet had time to fit it. Has anyone else had this belt dusting problem? Especially with a Balmar upgrade? BTW, the original owner who fitted the Balmar didn't upgrade to a double pulley, double belt and I am reticent to go to all that effort.