Hemlock when dry becomes very brittle. The grain structure is two diferent colors as you know. Light soft grain and very hard darker grain. I think you may find the soft grain to be too soft and the top will tend to split there.

This was the case with some very dry radial sawn floor board in my home. The boards where 6" by 5/4" full thickness and if they where in the house when it was built (1854) they split out overtime.

Now I know you are thinking "150 years, what the hell is he whining about?"

I'm not whining, I just wanted you to know the stuff just isn't very dependable.

Don