My bow pulpit (1990 2755 SCR) is a bolted on platform affair and very secure. I looks almost identical to what's in your picture. Not sure about 265 lbs on it, but 190 lbs makes no bend or movement in it.
As an anchor chain tensioner I use the heavy rubber tensioner cords that they use on trucking tarps etc. They don't mark the deck, are UV protected, are good in any temperature, the end hoods never rust. I put it around the deck cleat, then lead the hooks back to the anchor ring where it joins the chain. Holds the anchor nice and secure no matter the conditions. Best of all - they last for years and are not expensive.
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