If it were mine ... I'd make 'smart' cuts as needed to then allow it to be bolted back together the strongest that I could. Those supports from the floor angled up to the transom are called the 'knees' and I'd keep them affixed to the floor, as with that side flange, you can then bolt them back in place up top to the new transom.
Simple way, once you get the 'top cap' out of the way:
Ah well, they can't last forever now, can they? My transom on the vintage '78 12' Starcraft skiff was starting to show her age. I like this hull, with the way the ribs and chines were formed, she's as tough and stable as any 12-footer I've ever been on. The stern width was > 49" so I ended up...
Now this post here may be overkill
, but this is how I do replacement transoms and maybe it will give you some ideas.
Here she sits, a mint (for her age) 1976 Holiday 15’ model. All original and 1 owner, where the family is now on the 3rd generation enjoying the boat. The only issue is, the transom has now gone soft. The boat was in VA on any Army base, where they even have a boatyard and boat ramp to the...