I’m not so sure about this being a home made job. After cleaning it up a bit the only way I see it being home made is if someone had a hell of a machine shop not to mention a way to make some nice castings. Possibly the motor was added to what was originally an outboard with an engine attached. Here are sosme closeups.
Seems like I seen an "Ad" before in an old magazine
on making your own trolling motor with an automotive
generator. Not sure if they were selling a kit or not.