I think yours, from the pictures you posted are 1/2 inch, mine was.
I used exterior grade plywood on my transom, but thicker and with the biaxial sandwiched between ... Should be strong enough to hold a 150 HP motor.
Also mixed some polyester resin and styrene, 50/50 and sealed all thru hull / transom holes. The mix is as thin as water and soaks into wood.
Tabbing is strips of fiberglass, layed down around edge of transom / floor (tabbing & tabbing2)
AAAAaaa....
The wood and resin question ....
Polyester : our boat were made with it.
Vinylester : newer, stronger version of polyester.
Epoxy : strongest , but you can't put poly or vinyl resin over top of it won't stick, not a big deal though.
Exterior grade : cheapest, if covered and sealed should last 30 to 40 years.
Marine ply : low voids, better glue, all holes should be sealed though, might have to be ordered from your local building supplier.
Composite : never rot, light, easy to cut, can be expensive.
Watch video Doran posted, read some the rebuild threads on here and CGOA and talk with your local glass supplier.
Shawn & Joe have some rebuild threads on this site.
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