I remember having to do that manually on our emergency generators when I first started work. Watch the syncroscope and operate the breaker at about "5 to the hour". This allows time for the breaker to actually close. I can't remember the output of the generators but rated in 100s of kW The motive power was an "English Electric" 6L marine diesel, running at 375rpm; compressed air start.
Speed of generator 2 was always adjusted such that the syncroscope was rotating slowly clockwise.