San Juan 28 Transom too thin for the outboard I installed

Hello I’ve made a mistake on installing a 9.9 4 stroke to my San Juan 28. I created a wedge from 3/8" aluminum to compensate for transom angle and attaches an outboard lifter to it. The wedge is bolted through the hull with a 1/4 aluminum backing plate that is about the same dimensions of the wedge. Everything is attached with 5200. I used the materials for wedge and backing plate simply because it was scrap that I had laying around. Unfortunately I had no idea that my transom being about 1/2" thick solid fiberglass wouldn’t be able to support the 9.9 until I installed it and noticed the transom moving quite a bit with a small amount of pressure from my hand on the top of the motor. Upon further research I realized fairly quickly that I need about 1 1/2" of material. Any ideas out there for beefing up my current design without battling trying to take apart the 5200.

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it really needs to be beefed up from the inside, if you glued down the backing plate it may be real fun getting it off, you probably need to see about getting some core material and then glass over it from the inside. I would choose a core material that will not degrade with time or moisture. Best of luck!