Go new, dont even think about rebuilding
Go with the new.
Check out Beta Marine and other suppliers.
Select size and footprint to fit existing mounts, should be easy.
Select transmission to get right hand vs left hand.
More HP will require different prop. Don't mull over it, just get the new right prop.
You'll be shocked at how much better the new motor, new prop, and new HP level will improve your life aboard.
Ensure closed loop cooling.
Tear down the old motor to reduce weight and chuck it over the side (lol, only if onthe hard). That was the 2nd best day of my boating life, getting rid of the volvo MD7A. what a wreck that motor was.
lots of rugs, and elbo grease and a few beers for friends will get the new motor in place.
Rebuilding that Volvo was the biggest waste of money I've experienced, second only to the stock market. lol