I need Transom Help Please!
 

So I've been rebuilding my 1975 MA, today we got to the transom area and we're hoping we would just have to re-glass the cracks etc. no such luck... The wood in the transom is soaked. In the 80's my Pops replaced his transom on 69 seacraft hull from the inside out. So we started that way. We have cut everything out so far and the whole outer shell is still intact. Looking on this site I'm seeing a lot of people have cut it from the outside and left the inside. Are we doing it wrong? Also at this point it's too late, Lol.
Next question is for the core of the transom has anyone used 1.5" NidaCore board? That's hat I was planning on using. Idk any help/input would be awesome and greatly appreciated. Also I have a 25" 1987 Johnson 140 for power... Do I need to raise the transom? Or can I leave it alone? Thank you.

I like to do it from the inside and think it is a better way myself but it can be done both ways and still be plenty strong if done correctly. I just like to leave the original hull shell in tack if I can. Also its easier to add thickness to it as well. The biggest advantage is there is way, way, less fairing.

If you want to do composite, Coosa is hard to beat but there are others that will work too. NidaCore will crush in under pressure from engine bolts so I wouldn't use that tho.

Height, I always add a few inches to the transom. Normally shoot for 26.5-27 so the outboard can have plenty of adjustment moving up to get the av plate out of the water while under way.

Just wants to thank you for the input. We went ahead and used marine grade ply. It was a lot cheaper than the Coosa. I am glad that we re-did it bc we were able to check out the stringers and they are not soaked at all so that was very reassuring. I am going to add some pics to show our progress.

Updated Pics
 

Glued and Screwed Two pieces of 3/4" Marine Ply than epoxied the outside... Glued/West System Epoxied to outer shell, it has no dried and we will glass it in.. More Pics to follow after the weekend. We have also completed the whole cap of the gunnel on the MA so hopefully we will have that put back on as well...