The star washer was a bit tricky but then I remembered an old trick - taking a socket the same diameter and putting a clamp on the rear end to stop the pin from sliding out the other end, it was a simple matter to tap on the star washer.
Alas, despite several intensive searches I was unable to find a similar smaller roller but a spare castor roller I had has sufficed.
In the meantime the block/tackle set up for the centreboard is now complete.
I've put on some simple ply washers to fill the gaps where I managed to mis-measure (see previous post) and now they seem to work fine. My only concern now is that the double block fits down inside the centreboard casing!!! Now given my mathematical inabilities who wants to take a bet on it fitting well?