When was the last time you changed your water pump impeller?Could be a piece of the impeller blocking the water outlet.Was the outdrive tilted the same each time,possibly pinching the rubber hose or the hose seperated.Maybe try removing the hose on the engine a try back flushing to see if water...
There should be a small wiring harness that comes from the engine to the control box that has nothing but the tilt and trim wires and trim gauge wires in it.Just tap into those wires,be sure to use sealed connectors so there moisture proof.
you are correct on the color of wires,blue/white is up,green/white is down the red/white is the power wire.are you using omc control boxes or something else.if the boxes are the same you can just switch the handles.
No way to lock it down,not very safe to run it loose,the engine will kick up in reverse.Might try a salvage yard for the parts to convert it to manual release.Whats wrong with your power tilt and trim.
That engine had a the lever pictured,a cable and a hydraulic cylinder.If you moved tye lever one way it would lock,move it the other way you could manually move the engine up and down.I not sure but I think those parts or nla.