I've said it here before and I will say it again: It is very difficult to look at a piece of wood and identify it as "sinker" wood. Thus I'm skeptical that some of these sinker claims are real. I live in an area that really does have sinker redwood. I know the people who recovered it and know it is legit. We are actually one of the primary sources. However, if I was buying "sinker" wood from an unknown source I would be... skeptical. This does not mean that the wood you have is not real sinker wood, but one must view such claims with slitty eyes. Plus, does one believe that wood lying at the bottom of a river gives it some sort of magical property? There are good theories behind such claims (mineral deposition, etc.etc.) and I won't say it ain't so, but I think the craftmanship and the shape of the ukulele has a lot more to do with how an instrument sounds than the amount of mineral deposits in the tonewood. Also, just because a crappy, wide grained piece of wood sat at the bottom of a river for 100 years does not a great tonewood make. From your description of the wood, it sound like good tonewood. Who cares whether it is sinker or not. Buy good sounding wood and don't get too hung about whether it is "sinker wood". If you can get hooked up with the real stuff at a reasonable price, go for it.