Yes, in the mid-'80s Ford changed to an oil pressure switch instead of a variable resistor, making the oil pressure gauge an ON/OFF gauge, so an "idiot light".
Switch is OFF under 5.5psi approximate, ON above 5.5psi, this Grounds the gauge and it shows 1/3-1/2, any movement of the needle is from changes in voltage, not oil pressure.
The squeal could be the Cam Synchronizer, it is located in the old distributor hole and on the 3.0l it is prone to bushing/bearing failure around 80-100k miles.
It also drives the oil pump, same as distributor did, so if it fails while you are driving the truck you could ruin the engine.
Good read here: Ford Ranger 3.0L Camshaft Position Sensor