You can pull the #1 plug and put your thumb over the spark plug hole. Now rotate the motor(remove kill switch and have someone tap the ignition switch to rotate the motor, make sure you are clear of anything that turns) until you feel the pressure push on your thumb while watching the timing marks. The compression on your thumb will let you know you are on the compression stroke. From here you can follow Jim's post on setting the initial timing.
Gone, out doing soft recreational past time with overpowered boat!