I wonder why they're square holes? Almost like they're designed for a carriage bolt for some reason. Maybe just casting holes? Could be just a by-product of the manufacture process with no real purpose?
IDK, that puzzled me as well.
Call them and leave a message also, at least I would. They always call me back.
I will if I don't hear back from them. This isn't pressing just wanted to figure out what the hell they were for.