da Rock

Forget the STEEL brackets. Simple fiberglas reinforcement would work and is going to be much lighter. Remember how the dense foamy flew? How would it have flown with additional stiffening. Or more exactly, how did it fly with additional stiffening that could have been lighter.

Read up on interference drag. It's the problem aircraft designers have with unstreamlined, 90 degree interior corners. The solution is often fairings. The fairings are perfect where you want the corner brackets for providing reinforcement that is economic of weight.

Consider also a wider structure from the fuselage to the wing saddle. The present slab of plywood introduces an interference drag where it joins to the fuselage, and compounds the problem just above there where the wing is going to be strapped on.

Remember the WWII Corsair? It used the identical engine the Hellcat used. The Hellcat's wing to fuselage joint had an interference drag problem along the upper connection. The Corsair, thanks to it's distinctive bent wing, joined the wing to the fuselage at right angles. Right angles aren't the perfect solution, faired joints are. Yet, the Corsair was significantly faster than the Hellcat. Everything else was basically equal. Not only was the Corsair faster, but it easily carried significantly more stores at higher speed as well. It wasn't the gull wing, because they actually are less efficient. Was it the Hellcat's less efficient wing to fuselage convergence? There really isn't anything else that differs between the two.

Consider again the TWO joints. Fuselage to pylon. Pylon to wing.

BTW, interference drag is also a minor consideration when deciding on where a wing's dihedral breaks should be. Every little thing can matter.