Mast step repair

I have a 37' fiberglass sailboat (1960's Buchan 37) with a rotten mast step structure in the keel. I need to replace the structure but would like something more rot resistant. The main reason for the rot is probably water coming down the mast (Poor seal maintenance). The step design is made of 4 pieces of wood running cross-wise, basically 4" x 4" trimmed to fit the hull/keel/top of lead ballast, and level on top to carry an aluminum load bearing plate that the mast attaches to. I'm thinking about replacing these wood structures with an equivalent built up composite structure, basically composite 4" x 4", with thick walls and a hollow or foam filled core. Vertical mast load is estimated at 11,500 pounds. Anybody have any recommendations on this problem/idea?

 

Replace it with exactly what was there in the first place and take better care of the mast boot and it won't happen again..

 

Yeah, 47 years with no maintenance is really good.