welcome aboard.
with a boat that was sitting for 8 years, you have to go thru a bunch of systems
since the motor has not been running for 8 years, you no longer have an oil film on the bearings. do not try to start it as you will have a dry start. the fuel in the tank has long quit being fuel, and the raw water impeller is now currently dried up like a dead spider.
here is what I would do
pull the drive. that allows you to service the raw water pump, replace the bellows and inspect the alignment, gimble and u-joints
while the drive is off, pull all the plugs, squirt some oil down each cylinder and let sit for a while
replace the engine drive belts
change the engine oil and filter
pull the distributor, using an oil priming tool, prime the oil system until you get good oil pressure.
rotate the motor by hand a few times (grab the belts and turn)
then install the distributor
install new cap, rotor, wires, etc.
clean all battery cables and connections
replace the batteries
set timing
using a small outboard fuel tank and not your built in tank, hook up to the fuel pump
insert a garden hose into the round water inlet of the gimble housing and turn the hose on full.
start the motor. once you get the motor running, then move on to installing the drive and cleaning the tank
pull the fuel tank inspection cover
remove the sender
inspect the tank. you may have to pump out some sludge, however you will need to clean the tank.
buy a fuel/water separator filter kit. most 3.0's didnt come with them. your going to need it.
then go boating