Having recently gone through a forced engine replacement about 600 miles from home, I'll pass on the highlights. The really bad news is you'll almost certainly have to buy a motor with common rail fuel injection, required for pollution control. Most of the fuel system parts that can be handled, more or less, while tied up somewhere are gone. The FI system is now controlled by a black box, the injectors are high tech marvels, and the common rail, feeding the injectors, is pressurized to about 30,000 PSI.
when we looked for a replacement motor, I was very emphatic about no black boxes. We looked at four Yanmar motor types. One was too big, the others were no longer available. We now have a Westerbeke 54 HP motor after starting with a 32 HP motor. We planned to pick up some HP, but not that much. You take the motor you can get.
The conversion wound up requiring replacing the 2" dia. exhaust system with a 3" dia. system, and the raw water inlet went from 3/4" to 1". No battery changes were needed; the existing house battery is quite capable of spinning the new motor.
Re-pitching the prop bordered on the traumatic. For reasons that escape me, the yard put the original prop, pitched for the 32 HP motor, back on the boat, even though I said we needed a new prop (age, re-pitching, log strike all put that prop at the end of its service life). It took, IIRC, three, and possibly four tries before we got the right pitch (the prop loads the motor to the point where wide open throttle spins the motor to its red line RPM and no more, and the motor doesn't smoke from being overloaded). I learned that there are all manner of handy prop pitch tools and spreadsheets that will conjure up a pitch, based on boat specs. They're a guideline and nothing else. There is a point in pitching where science gives way to art and experience. And the pitch for any type of boat isn't the same for all boats of that type. Every hull type and motor type is different, thus so is the pitch.
while I still think the installation was well executed, there were ...um... surprises. Notably, the house and start banks were hard-wired at the alternator. Other surprises have, mercifully, faded from memory thanks to deliberate repression or the mists of time. Assume you'll have some fun moments, too.
Good luck! You'll need it. :)
Eat more moose, 17,000 wolves can't be wrong...