Cleaning up Chainplate Fiberglass 

I would consider filling those with a sheet of G11 and fiberglass them in

I'd attack that with an angle grinder. Finger sanders are cool and all - but it's a slow tool. Looks like you have the room.

The difference from one side to the other is likely due to the rust -- the side with the crevice likely had a more significant leak, and once the rust began to expand it split the layers of the hull allowing the rust and rusty water to follow the gap in the hull. You should really watch Rigging Doctor's most recent episodes -- he is changing out his chain plates too, but he takes a deep dive into calculating the size of both the chain plates (length) and how the number of holes is calculated based on the bolt size that you are using. External chain plates do not rely on the bolts for strength, they rely on the friction between the chain plate and the hull -- that is why the length of the chain plate becomes crucial. Do yourself a favor and watch the last few episodes!!!

🦭

How much whiskey did they imbibe you with?