As for clamping the new transom in, I used every esixting hole in the outer skin I could. The motor mount holes as well as the drain holes. I drilled smaller holes than needed to mount the engine, so if they were off a little, it would effect anything down the road. I clamped the transom with 2x4s on the outside to spread the load. This worked great until it was time to take the clamps off. The cabosil seeped through the holes and glued the 2x4s to the boat, I had to chip the 2x4s off. So if you go this route, put some wax paper between the 2x4s and boat so it comes off clean.