I used some synthetic material to replace the grass rails on my Devlin Broadbill. It worked pretty well but it wasn't as stiff as I would have liked it to be. Scarfing two pieces of mahogany sounds like a good suggestion. I may choose to do that in the end.
This is what I found online about the other woods:
Red Grandis Eucalyptus
While the color is much more pale than genuine mahogany, red grandis is very similar in weight, density, grain structure, and the way it responds to most machining operations. The wood's color does deepen with age turning to a darker red much like mahogany.
Clayed Poplar
Thermally modified wood products have been used widely for more than 20 years in Germany, Austria, Norway, Switzerland, Japan and Italy for both interior and exterior applications. Centuries ago, the Vikings learned to overcome the shortcomings of natural wood by treating it with fire. They discovered that burning the surface of cut wood made it more resistant to the effects of outdoor exposure. It was only within the last century that Europeans perfected the thermal modification process. And by adding steam, found that the structure of wood was further modified, making it more impervious to rot, mildew, and decay. The thermal modification results in hardwoods with outstanding dimensional stability and rot-resistance. The ability of the cells in wood to transport water is reduced, resulting in water-resistant properties. The sugar content in the wood cells is also reduced, minimizing the food source for mold and fungus. These two physical changes in the wood result in a hardwood product stable and durable enough for exterior applications ? much as the Vikings used it.
Thanks for the advice, folks. I let you know what I decide to do.
Grace and peace,
David