If it were me I’d be posting this on a boating forum relating to the related make of boat. A lot of grumpy old boat wrench types hang out on those who shave hands on experience with those exact things.
I stick to the smaller stuff myself but have lots of wrenching years on mine and a couple decades of gleaning info from the net on fixing my stuff.
I know squat about boat trannys beyond stern drives. I’ve learned a lot though watching others suffer disaster after disaster. First, With a big boat like you are looking at here you really NEED to pay an experienced mechanic or surveyor to inspect it. Trannys can suck but big boats in particular die from rotten transoms and hull cores. They can be beautiful bit rotting internally from something as simple as an owner replacing a deck cleat and not sealing the mounting screw years ago. Transoms rot from silly things like changing a sonar sensor the same way. Decks suffer from rain rot , get a soft spot then it gets worse until you have to cut it out. That takes years too and isn’t often obvious. Did it live in salt water ever? Raw water ( bad if in salt water) or closed cooling (antifreeze) is a big engine factor. Stuff like this really matters. With all that in mind it’s a good idea to pay a pro who has the moisture gauge and experience. It might be the best$2-300 you ever spent.
If you already know or did all that fun stuff of course disregard. I can’t tell by your post what your degree of experience is with these things and just don’t want to see yet another web posting by some poor owner who got taken by a beautiful boat with hidden $$$$$$$ issues. What make / model is it anyways, how many hours run time.