That's a good point because the engines are easy to remove from the bike. On the other hand, this cylinder head nut tightening job is extremely easy to do with the engine in place.
1. Loosen top engine mount bolt on head.
2. Tighten the four flange nuts in a criss cross pattern to specified torque of 18-22 N-m or 1.8-2.2 kg-m or 13-16 ft-lb.
3. Tighten the top engine mounting bolt (at the top of the cylinder head) to specified torque of 30-40 Nm or 3.0-4.0 kg-m or 22-29 ft-lb.
Job done. Go back to the pool and enjoy the rest of the day.