When I had my sterndrive in salt water, every spring there was small pieces of rusty steel in the bilge. Lots of non-critical items would succumb to rust. You might look around for some of that. Also, the cover over the ring gear, next to and down from, the starter can rust and rattle.
Any idea what oil was put into the engine?
The oil pressure switch grounds when there is no oil pressure. Look for a "Peppermint Patty"-like device with a single wire on the block.
Have you removed the transfer cover? That will give vision to the cylinder. A bore scope is also good, however, you are going to need to pull the piston out anyway.
The rings will likely be stuck in their grooves, killing the compression. If the cylinder walls are good, still with a...
Years ago a friend had a 25 foot cruiser. He put a 30G drum with a spigot on his pickup (with chocks), and filled it at the gas station. He had a long hose from the truck, downhill to the boat.
It is often #3 that overheats and fails. Make sure the carbs are clean and the water pump impeller are changed every 3 years or sooner, if you hit suck sand into the motor.
The shift slider is bolted to the powerhead. As such, the linkage from the shift slider to the shift arm needs to be released. The rubber slider can come out of the slide track to accomplish that. You can also remove the bolt holding the shift arm to the slider linkage.
Mercury's throttle cables push the throttle closed. You want to have the cable push the throttle closed, and then add some preload to the throttle cable to help you feel neutral. Make sure the idle stop screw is set properly.
A 28 footer with a SBC is marginal on power, IMO. They ought to come with BBCs. Normally on those kinds of boats, with the correct prop, everyone must go into the cabin until we get on plane.
The correct prop is a must. Careful placement of load is a must. Try to load the bow as they are...
Mercury shift sliders move forward for forward. Set the engine to neutral, set the control to neutral and adjust the shift cable barrel nut (engine end), so the cable fits the shift slide position.
The way I understood it was that a V6 or smaller FWC engine could be cooled by the outdrive pump, but a V8 or larger FWC engine needs a belt driven thru the hull water pump to cool the heat exchanger. Is that correct?
In case someone does not know, a 1/2 FWC motor needs a heat exchanger in the boat to function. A raw water-cooled motor does not have a heat exchanger in the boat.
Remember your outboard drains completely after you pull it out of the water. You are dealing only with the salty residue from whatever residual water (a few oz at most) remained or evaporated.
If you run it on a flusher, until the thermostat opens, and then a bit longer, the salt will be...
