Here, I am working out how much space is available for the primary part of the second layer. I'll need to make 2 small pieces for the "wing" portions at the top edge, then glue it all together.

Continuing on the previous thought - this will be a multi-piece transom (4 to be exact). With the extra glass and reinforcing it will be stronger than the original transom - MUCH stronger. If I could afford epoxy instead of polyester resin, it could be even greater strength. However - the original transom was rated for 90 HP and I only have a 70 HP motor, and I have no intention of going over the hull's engine rating. Even if higher grade plywood gave me a 50% gain it would be pointless - nothing but overengineering for the intended purpose.

Once again - if I can't AFFORD the materials nothing gets done and we have no boat.