Frank, for a floating tenon just mill a 1/2" or 3/8" mortise in the butt and extension, fit a tenon snugly in the mortises, glue and clamp every thing together. I think it would be best to use walnut for the tenon. If my memory is correct I think Chuck H. used this on the Browning stock when he did a butt transplant a while back. It is a common joint used in cabinet work.

Jim

I learn something every day, and a lot of times it's that what I learned the day before was wrong