Some thoughts, but no conclusions:
My original decal on my last Seafari (1972 O/B model) clearly said Max HP = 240. Not 175. And it was built at a time when the most powerful outboards you could buy were the V4 125 hp Johnnyrude or I6 115 hp Mercury.
The transom cutout on my 1st Seafari, a 1973 model, was clearly made for twin outboards, as well.
I rigged a new 1984 factory custom-built 20 SF which was factory placarded for 250 hp back in '84, and we rigged a Bridgeport Mercury on it, rated at 240 hp.
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Common Sense is learning from your mistakes. Wisdom is learning from the other guy's mistakes.
Fr. Frank says:
Jesus liked fishing, too. He even walked on water to get to the boat!
Currently without a SeaCraft 
(2) Pompano 12' fishing kayaks
'73 Cobia 18' prototype "Casting Skiff", 70hp Mercury
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