Like Bill says, there are many subtle/little differences between the 25hp vs the 18/20 models of that vintage.  But, the changes vary through the years, so the only reliable guide is the proper parts book.  The important thing is to use the proper pieces/parts described in the parts book.  It is super easy to accidentally substitute a piece from the 18/20hp models only to end up in “head scratching” later.  I’m guessing this powerhead had never been split before, so it is somewhat safe to asssssume that the parts are original, but you never know…

OK, sounds like the damage you found is enough to affect compression and proper crankcase sealing.  Like Bill says, these 22CI blocks suffer from sleeve/casting separation when used in salt water.  So, please have a close look at this area.

Finally, this engine appears to use the strange upper bearing oil recirculation system that OMC used for many years.  So, my question is did you find an oring around the outer diameter of the upper bearing that would seal the area between the bearing case and block halves?  My guess is there was no oring there when you disassembled it, which is strangely “correct”.  Yes, this doesn’t make sense, unless you understand how that recirculation system is supposed to work.  Adding an oring to the outer diameter of the upper bearing is a mistake easily made for sure.  Unfortunately, adding that oring will block off the recirculation port and might very well cause excess oil to build up in that area.  So, please take some time to look over the various oiling holes and intake port/gaskets, to make sure the area is properly cleaned and set up prior to powerhead reassembly.

Again, feel free to post pictures of anything you have questions about.  Pictures can be worth so much more than words.