My old parts catalog calls for part # 8010121 or a 3/16" X 5/8" with a backup washers. Be sure to buy enough rivet caps, part # 08011291. The guide states (9) required.You may choose more.
Now that size seems a little short to me, so I would get the longest rivet that fits the rivets caps if it was me and be sure to use those backup washers or stainless fender washers if they fit and as you could reach.
Use your imagination to reach the backside of the rivets inside the hulls as a backup.
You may have to trim fender washers to fit into that tight pocket under deck.
I remember adding some rivets to my 21SE tramp track and that what I did.
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Bill 404 21SE
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