Ok I’m going to speculate here.
The original rope sheave got
broken and that is a replacement.
It came blank and someone
stamped it with the motors serial #
that’s on the block.
Your tiller was first used in 1937.
1936 is different. With that low
a number I would speculate it to be
a 1937 Model 571-10 and it should
have this exhaust. Everything is the
same in 1938. The model # and exhaust
changes in 1939.
A "Boathouse Repair" is one thats done without having tools or the skills to do it properly.