Looks like an homemade pair. The bolts look like old lag bolts About 3/8” X 3” long. The wood looks almost rotten and is split where the the bolt are. The Cannon it self maybe it was was somewhere else and they moved it and put it here for a display!
The cannon was moved to its current location and mounted on the carriage built of strong solid oak sometime between 1935 and 1955, it has not been maintained or refurbished since then. That is still standing is a testament to how strong the oak was and to how well, if not historically accurate, the carriage was built.
The question that I posted was if it was possible that the cap square was actually made pre 1865.
I think ucvrelics has addressed that question.
If anyone else has information concerning my question, whether they agree or disagree with ucvrelics, or have anything relevant to say, I would like to hear from them.