If the engine is running for only a brief time, make sure there are no air leaks in the fuel system otherwise the fuel pump may be sucking air, not fuel.
Pressure check fuel lines back to the tank, disconnect at tank and carb, plug end at tank at put a couple pounds of pressure on the fuel line and make sure it holds pressure. A lose hose clamp or maybe the o-ring in the water separator cup could introduce air into fuel line.
Grab a gas can and run a hose directly to fuel pump, this is a process of elimination (not this, check something else, keep going till discovering something that was overlooked).
You began this project b/c the boat wasn't running correctly, maybe the original problem still exists and you're getting closer to finding it. Of course you have to be careful not to create new problems, like dropping something into the carbs that might make it's way into the rotary valve. I find it unlikely you did but that doesn't mean you didn't.
Squeeling, like dry metal on metal may have come from a dry engine, one that doesn't have enough oil? I don't think it would be a bad idea to consider mixing up some fuel in a can at, say, 32:1 (1oz:1quart) and run a couple hoses, (supply and return) directly from the clean gas can with mixed fuel, to the carbs. Be aware of the fire hazards this might present and prepare accordingly. At least this way you'll know there's oil in the fuel, until you can eliminate other possibilities from air in the oil pump or something. Could be, the oil pump isn't working, or maybe a screw in the rotary valve, process of elimination.
Stop and think, remain calm, backtrack, double check, all that stuff. You've gotten this far, I think you're just overlooking something simple.
Once, after a project similar to this, a friend of mine placed his gasoline-soaked clothing into has clothes washer and it caught fire and blew up singing his face. Be careful and take your time, think things through, don't get flummoxed, take a break and squirt some oil in the carbs or cylinders. These engines just love small amounts of oil, like I like eating lunch.