Johnson/Evinrude did a jet drive unit that bolted on in place of the bottom gearbox assembly.
The OMC workshop manual I have kicking around for 150 and 175HP 60deg loop V engines shows it in detail and has a full strip down etc.
The manual dates from the late 80's or early 90's, I presume they must still be out there somewhere secondhand or old stock, but might take some finding.
Be interested to know some more just out of curiosity.
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