Michel wrote:
My casing looked exactly like Gerald's, only a lot dirtier. But I had a UK built F33/35 catketch like Gerald. Perhaps the F28s were different, but I agree with Gerald that the wood is probably a foreign object in there. If you could make some photos, together we could perhaps figure out what the purpose of these blocks is. Reading your description over again, the blocks might be stopper blocks preventing the board to hit the (rope) blocks when the board is pulled fully up or preventing the rope blocks on the top of the board to be smashed into the fixed rope blocks when hitting the sea bed with the board fully up.
My current theory is that it was some remnant of a ground system. The bolt holding the wood was one inch stainless and off center in the trunk. Still a mystery!