RE: Goldberg Ultimate 10-300 build
Looks nice!
I would put a couple of hardwood triangular supports under the ply bracket. And consider a couple more bolts on that UC... My recomendation would be two M4 (or similar) on either side pluss one in the middle fwd.
A hard landing will bend the UC backwards, forcing the front of the UC on the bracket up.
Picture showing my ZN Synergy UC bolts.