you bought a boat with the merc 470 motor. start saving for repairs
also start googling merc 470.
prior to even considering taking that boat out
first, pull the drive and check the alignment, gimble bearing, u-joints and bellows. while the drive is off, do a full drive service (impeller and gear oil)
then move on to the motor. you will want to change the coolant. once drained, you will also want to pressure test the cooling system
if the cooling system holds 15psi for pretty much ever....
then move on to pulling the plugs and performing a compression test. do you have between 135 and 150 psi in each cylinder, yes or no. if yes, then move on to changing oil. if not, and two of the cylinders have really low compression, buy a factory mercruiser head gasket. pull the head, clean up the deck and install a new head gasket
pull the sender from the tank and clean out the tank. after 2 years the fuel that was there is no longer fuel
verify the anti-siphon valve is functional and not gummed up
sitting for 2 years, the carb should be pulled apart and rebuilt.
then move on to the ignition system. this motor has points. so file them, then gap them to .018. then using a dwell meter, make sure your dwell when cranking is between 28 and 32 degrees. then set timing.
failure to perform this step will have you cranking without spark
now, you can fire the motor up on muffs.