rotten stringers

Just purchased a 1979 V20 with the stringer outdrive. Have purchased a rebuilt outdrive only to find that the main stringers of the boat are rotted / hollow! The engine stringers seem to have been re-done and are quite solid. The rotten stringers are comprised of dry fragmented wood in the fiberglass stringer enclosures. I am contemplating removing the floor, chopping the top of the stringers off, removing the rotten wood, matting the good wood ends with glass/resin and then pouring seacast into the hollow stringers and re-capping....

Any opinions, advice, seacast info would be greatly appreciated!

thanks - John C.