PD - some of the American part suppliers websites like Crowley have serial number lookups on their home page, doesn’t work all the time but usually good with Mercury stuff.
Smagu - Is that the one that was on DoneDeal a couple of weeks back, in Kerry maybe?
If the transom is up to it a plate would work fine. Did something similar recently for a friend, he wanted to upgrade but couldn’t find a decent 20” motor, eventually found a nice 25” so used a manual Jack plate with a small setback, it added a little extra weight but easy enough to manage.
That A frame doesn’t look like an original, they were taller and narrower, but easy enough to modify if needs be.
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