For reason I won't go into here I am in the process of removing my lifting plate from my 24ft wooden boat. This has left me with a 3ft long and 5" wide hole in my iron keel. Of course I know need to fill this hole to make the boat watertight. In filling this hole I also need to add some ballast to this area to replace the weight of the lifting plate. My thoughts on the job are as follows:
To hammer a peice of teak from the bottom into the hole so it is a very tight fit and seal this in. From the top put in lead bars to help with ballast. This next point was from an old boy down the boat yard, Melt a lot of candle wax and pour this into the hole which will seal the lead bars and stop them moving around !!!
At least with this setup it would be reversible if needed.