[HardlyDangerous]

Water in the fuel/frozen fuel lines?
dump in some gas line anti-freeze and pray for a warm day . A hair dryer on the carb will thaw it if there is water in the float bowls.

If it has a manual set automatic choke push it right to the floor once, then let off then 1/2 way down. that should set the auto choke. then don't touch the throttle again until it starts

Take off the distributer cap and make sure it's nice and dry in there, clean up the contacts a bit. Check the timing, if you have spark, fuel and compression it's going to run.

BYW change the oil in that old boat and put some light winter oil in there to help it crank over easier