Find or getting appropriate sized bolts made up

That's the one. Well, one of them. Another one at the top and two more on t'other side!

My boat has the similar type of fittings and I had made some new pins to fit the reamed out holes to try and stop the knocking. It was only partially sucessful as nothing was 100% in line and possibly like that from new in the 70's. The knocking is reduced but can still happen in the right conditions.
 
I would try to make that only move in either the rudder OR the hull fitting, not both.

That's how it is. The bolts are solid against the rudder bracket. They only move within the hull fitting. I drilled out the hull fitting and fitted a nylon bush, but unfortunately its internal diameter is just a bit too big so there is still play between the bolt and the bush.

So, best solution seems to be to get appropriately sized bushes made up.
 
OK. This is the best option, in my mind. Get some bolts with plain shanks. Get some some tube (brass, bronze, whatever) with the same ID as the bolt OD. Cut the tube the length of the U bracket jaws on the transom (including the material. ie: to the top and bottom of the bracket) Drill (and ream) the brackets to make the tube a very snug fit through the holes. Drill and ream the gudgeon holes to fit the tube OD with a tad more clearance. Assemble and bolt through with a washer top and bottom.
The brackets and gudgeon will never wear, only the tube, which if you bought some spare, you can replace.
 
OK. This is the best option, in my mind. Get some bolts with plain shanks. Get some some tube (brass, bronze, whatever) with the same ID as the bolt OD. Cut the tube the length of the U bracket jaws on the transom (including the material. ie: to the top and bottom of the bracket) Drill (and ream) the brackets to make the tube a very snug fit through the holes. Drill and ream the gudgeon holes to fit the tube OD with a tad more clearance. Assemble and bolt through with a washer top and bottom.
The brackets and gudgeon will never wear, only the tube, which if you bought some spare, you can replace.

That is pretty much exactly what I did with plastic water pipe. Most domestic water pipe is polybutylene which has low swell.
 
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