When doing pressure test always squirt some lube innthe cylinders like wd40 or even pb blaster , if it hasnt been warmed up best option is warming up first then testing but ill assume thats not a option for you
Bayliners are just like any other boat with wood in them stringers and transoms , they rot esp when abused and left un atended to fill with water, biggest thing is bayliners were cheap lots of folks bought them as a first boat and didint treat them as they should but again any boat that has...
Thing to remember also is stress points, as others have men tioned, as you change structure of boat think of where stress will be I'd also argue the rear corners of a outboard transom are probably reinforced as well since that's a transfer point of stresses
here is what you would need to do
1 remove all existing i/o equipment
2 gain acess to the transom , personally id decap boat to make that possible,
3 unskin inside of boat and remove existing wood from transom leaving outer skin
4 install new wood proper thickess or make a form and pour in a...
not sure if its that hull but i remember something about a bass boat manifacture doing this purposly so it acted like a trim tab does, again not sure if thats your hull or not