Ok do u have any suggestions on getting it in in one peice don't know if I can get the top off as I am only replacing the transom the rest of the boat is solid
I doubt that the stringers are solid. you should do some test drills. usually the stringers rot first, then the transom rots, and last the floor rots.
drill into the stringers about 3/4" deep with a 1/4" drill bit about 1' above the hull, and about 6" back from the first bulkhead in front of the motor. drill about 3 test drills on both the port and starboard side. if the shavings come out light colored and dry, then fill the holes with epoxy putty and continue. however most likely the shavings will come out dark colored and wet indicating the stringers need replacing as well.
you cant add another layer. 1.5" of wood is your target. no more, no less total transom thickness of 2.00 - 2.125