Don,
I replaced the transom in my 1995 Lund 1775 about 5 years ago. I looked at Coosa but went with MDO for cost reasons. At the time Coosa was something like $600/, too much for me. Technically though, Coosa is far superior to wood in that application. With MDO my total cost was around $300.
Check with Lund as I think they may have replacement transoms for sale - depending on year or model.
My latest boat purchase is a Black Duck, Cromis flats skiff built here in Rockport, Texas. They only use Coosa board for it's superior stiffness and light weight.