"Disconnect the coil when hand
"Disconnect the coil when hand cranking. If it hand cranks, w/coil wire grounded, connect the muffs w/water running and crank the engine 10-20 seconds at most to build up oil pressure. Repeat after letting the starter cool for 30 minutes. No need for gaskets but new belts would be good. Change ALL fuel filters and add a pint of SEAFOAM to the fuel tank before adding fresh fuel. Replace spark plugs if dirty.
When was the OD impeller last changed? It should probably be changed due to dry rot. Was the OD oil changed? Check it and the level at the vent screw. Running on muffs will not tell you if it is pumping water; the hose is pressurizing the cooling system."
Fix minor things (replace wear items for preventative maintenance.) that cause major problems before they break.