Looks really good. I keep thinking of something simpler, since I don't have as many interests as you do.
The section where the 45 slot is cut looks like it has less bending strength than you might need. I guess it just depends upon how you load it.
Good luck

: Hello all,

: Well it's not really finished yet, but here is what I'm working on.
: It's a stand for kayaks, surfboards, SUP's, and all sorts of
: other projects. The 90 and 45 degree holes are for shaping
: surfboard rails- putting the board at a convenient angle for
: shaping rails. The stand also allows for a kayak hull to rest in
: the middle gap for planing/sanding/varnishing. The stands are
: made to slide onto a 4x4 and will be height-adjustable. The flat
: part is for surfboards but also works for holding other flat
: items, and I can put my work table across it when I need extra
: table space. There will be carpeting to pad the slots and the
: top part.