Simple things usually work best. That's what I believe, anyway.
So, when I was trying to decide how to remedy the problem of the oars hitting the side of the boat and getting knocked out of the oarlocks, I looked for the simplest possible solution.
The goal was to raise the oarlocks enough to give the oar adequate clearance over the sheer... without having to move the oarlock sockets and drill more holes in the sheer clamps.
This is what I came up with:
Half-inch spacers that I made from scrap mahogany. These raise the oarlocks about as high as possible, while still leaving enough of the shaft in the oarlock socket for the whole thing to function well.
It's not a perfect solution, as the oars do still rub against the side of the boat slightly — that is, if you're rowing from the rear thwart. From the forward thwart, (which is a better rowing position, anyway) the oars clear the side of the boat just fine. For as little as I expect to be rowing this boat, I believe this arrangement will work just fine.