Interesting to see this, as I have two Boucher engines myself (see photos here). I was not aware that this engine was made in several sizes. Mine are both the same size, with the odd bore size of 15/16th. I have seen few others, all were shown mounted on boats, and having the same metal name plate as yours. I believe that maybe only the engines sold with complete boats had the name plates, and that others were sold in some sort of kit form. One of these has the exhaust pipe attached internally (somehow), the other exhaust has a more typical threaded attachment that screws into the valve chest externally. I got these separately, as-is.
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