The block was too large, the epoxy didn't stick to the chin interior because it wasn't roughed-up enough. So, it wasn't too difficult to tear the thing apart.
This time I cut the block to half its size. I roughed-up the chin interior much more. I used more Magic-Sculpt and wrapped it over and under the woodblock.
After the epoxy hardens and I'm convinced everything will hold together, I'll use paper clay to sculpt the full jaw piece.