I have done one engine install in a boat and a couple in cars. The boat was replacing a Yannie YSE8 with a YSM8 - basically the same engine, just "Mark III" kind of thing. I did it alone and it took 5 weeks of evenings & weekends. It is amazing how much time you spend running out for fuel lines, new lag screws for the mounts etc. etc. etc. Lining up the shaft is very time consuming as well.
I wouldn't want to do a full on swap in a sailboat unless the engine access was VERY good. Trying to swap an engine in one of the boats where the original was installed before the deck went on would be an exercise in self inflicted insanity.
I did a swap in a car once - it was GM to GM so I could use all factory parts (Chevy into BOP for the car aficionados here). Even THAT fairly minor level of "custom" was maddening. starter on the other side of the engine meant custom battery cables. Fuel lines down the opposite side of the car meant custom lines were needed, flywheels had different bolt patterns than the converters etc. etc.
That was with a full hoist equipped shop too - doing it inside a sailboat would be more than I'd want to take on and I'll take on WAY more than I should.
Rebuild the 2QM or find another good one and save yourself a HUGE amount of grief and expense.