What is the normal oil pressure reading on a 1992 Lebaron

The oil pressure sounds fine. It, and most gauges, stay about in the middle for proper working order. Of course the pressure will be higher when it is cold until the car warms up.
If the Anti-Freeze ahs not been serviced I cannot stress how important a full flush and even a pressure test with a new thermostat and cap is.
I have seen so many customers lose cars even when they have changed oil, but neglected to change anti-freeze every 2 years or 60,000 miles. It can lead to a head gasket failure or even a full engine rebuild.
So, it sounds like you have a good thing, just don't let any of the service items get overlooked as they are all very important and can lead to major repairs.
A thousand dolars in maintenance will save a thousand dollars in repair.
I believe we have an article that does the math in the coolant section.

Fill the coolant and see what happens.
As I spoke earlier not changiong the anti-freeze can blow a head gakset and cause problem with coolant getting into the firing chamner and oil getting into the coolant and oil leaks in the system.
You may want to replace the Oil pressure sensor as the car has sat a lot and it sould be failing.
It will rise and dropp with RPMs. As long as it reacts and the check engine light does not come on it should be okay.
If the light does come on turn it off immediatley.
I think you shgould tend to the cooling system soon as it may be the source of some of your issues.

If you don't mind me sticking my nose in here, you're asking about an engine problem but haven't bothered to list the engine size. These cars came mostly with the Mitsubishi 3.0L engine and on those, 6 pounds of oil pressure is acceptable at idle. That is WAY too low for other engines but for that one, the oil pressure sending unit is calibrated for that low pressure. There was a common problem with the sending units reading erratically. They caused the gauges to fluctuate more than normal between idle and high speed. Some occasionally even caused the gauge to drop to half of its normal reading, then bounce back up when engine speed was increased. A new sending unit will solve that.

My old rusty trusty '88 Grand Caravan daily driver has the 3.0L engine and just turned 394,000 miles today. Oil pressure has never been a problem and I'm not going to tell you how many years it's been since I changed the oil. The doctor is right though about changing the coolant. The additives that neutralize the acids that normally build up in the system wear out after about two years.