23 CC minty green!

[Blue_Heron]

You may want to hit it with one more layer of structural glass (rov/biax). I used 2 1708 and 1 rovin plus tabing and knees on my inside. Others may have opinions on this?

I agree. In general, you want to use the same thickness of laminate and the same thickness of core as the original transom. The transom's resistance to bending loads depends mainly on the inner and outer skins, their bond to the core material, and the thickness of the core. If your transom started with a 3/16" inner laminate, you should build it up until you have the same thickness on the new skin. A thicker laminate will also help to spread the crushing loads from through bolts.
Dave