transom thickness

hey guys new to the site. picked up a '79 cc, transom is solid but wavy. thickness goes from 2 1/4" to 2 1/2" and is sucked in around bolt holes.
what is the maximum thickness the transom can be. don't have outboard
yet but my buddys got a '99 johnson 150hp for me. would like to have
transom ready when motor gets here.