The "265" you mentioned sounds like the Merc version of a 350 Chevy. If that's the case, you're lucky, because they're a dime a dozen (parts are cheap) and easy to work on.
The mounts shouldn't be a big deal dollar-wise. Just some heavy labor. I'd be more concerned about
why they broke. Make sure it's just the mounts and not the stringers. It seems a little weird that a boat would sit for 8 years just because of busted mounts. Like Badnews & Tom said, you're gonna have to do a lot of nickle & dime stuff to get it ready.