I kept to my word, and am creating the piece to replace the Balcongerat on the forward edge of the bottom keel. During the timeframe I am building U-505 for, it did not yet have the Balcongerat.
I used sheet styrene for the "fill in" piece to cover the hole in the hull, and curved it to match the hull curvature.
Small pieces of square strip styrene are used to create "shelves" to hold up the forward end of the piece, so it is level with the outer hull.
For the replacement keel end, I used four (4) pieces of Evergreen #258 rectangular tube, 2 high/2 wide. This turns out to be the perfect size to match the keel on the hull !
The shape of the piece is complex as you can see by the other end of the keel.
After cutting the keel end piece and roughly shaping it, I filled it with putty and set it aside to dry well. Then I will begin the sculpting it into the proper shape; I may have to end up using epoxy putty... we will see.