I wouldn't use those extenders. One solid piece is stronger than two plates due to load shedding issues. And frankly I don't think $75 is a very good price.personally I would go with a single wide plate, with the attachment point hanging just off the transom. So there is nothing that could contact the legs once installed. For a backing plate I would use G10 at least 1" wider than the plates, epoxy bonded to the hull, with fender washers backing the nuts.
Without knowing the layup schedule in this area I couldn't guess how to calculate the size (Brion probably does). But a wider strap provides more contact area and thus more friction, as well as spreading the load over a larger area. So the question in my eyes is what other constraints do you need to deal with? Is there other equipment that needs to be worked around, aesthetic issues that need to be adressed, or is the entire side of the hull available?
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