Also.....that port is tapered so it is smaller near the bottom....if you could grab that bolt head and raise it up higher, then turn it sideways, might be able to just walk it out of there....worth a try if you haven't already....
That's the idle exhaust port.....the broken bolt head could have fallen down in there when somebody had the PH off for some reason.....didn't see it when they reassembled. Won't hurt anything where it is now....probably been like that for a while. Not worth pulling the PH if there are no...
It looks right in your first pic.....there is a metal collar that is installed first with the cupped side facing up, then the rubber seal is seated down into the collar. When the shaft is pushed into the hole it seals out water. Some say it is not really necessary and will run fine without it...
That's where it goes.....if you take that bracket off you can slide the water tube out, put the grommet in that hole, then slide the tube back down through it...might have to put some lube on it if it is tight. Keep it straight when putting it back in and will go right back into the pump.
Seems excessive.....not 100% sure on your engine but I believe the PH would have to come off....did on mine. Would rule out all other leak points first as this would be a last resort for sure.
If you can't see a leak inside the cowling, there is a seal on top of the water tube where the water enters the powerhead.....if it was leaking bad enough could be the cause of the overheat problem...not enough water pressure.
https://forums.iboats.com/threads/synchronizing-carbs-and-timing-on-a-75-150-chrysler-or-early-force.420505/ The late Frank A. describes idle screw adjustment beginning with step #8 in his lync n sync thread......
