2 prior threads with discussion on B30 fixed, lifting and swing keels. If you list your question on trailersailerplace some good responses might come out?
www.trailersailerplace.com.au/phpBB3/viewtopic.php?t=6505www.seabreeze.com.au/forums/Sailing/General/Farr-Binks-B30-Fixed-Keel?page=1Would assume that a plug could be made of glassed ply with (say) 50mm vertical height perimeter timber around the 2 sides and rear so that it could be located down into the case without twisting - held in place by 2 vertical ply gussets which are secured to the plug upper surface suitably fore and aft spaced and bolted to the case top to neat fore and aft stainless angles each side of the case able to be undone easily? Do you have a photo of the swing system and the rear of the case when the keel is fully down to show what is there and what might be in the way of the plug? If you have the table arrangement in one of the links that would need to be modified?