Awesome, thanks Roger. Locust seems much like Oak or Maple in many respects, so an Fv value of ~200 psi seems reasonable to use.

The joint I described in my second post is indeed much like a dovetail. Based on the above Fv value, I do need the restraining effect of the decking---the dovetail itself could only hold ~600 lbf (about half of what is needed).

The mortise in my first post has a shear area of ~5 sq. in. if I include only the *bottom* plane of the mortise in the area calculation. Including the sides as well gets me up to ~12 sq. in., for ~2400 lbf, about twice what I need. Is it OK to include bottom & sides of a mortise in the shear area calculation?

Thanks again for your valuable input!
David