Please advise.

My recently purchased still in the wrapper 88 Turbo Thunderbird has an oil pressure gauge that almost immediately shoots to nearly high on start up. Then goes back down around 3/4 high upon warm up. Never goes to normal as it should. The oil is clean. The turbo boost is fine. No rough idles. Overall it is 28 year old beauty with 36k miles original that spins like a new top. What would be the cause. I just brought it home. The previous owner had it for 2 years -and put less than 500 miles. I believe the car has sat a lot for the last 20 years. Thoughts?
Maybe it just still has good oil pressure?
The gauges on these cars are glorified idiot lights at best. They might have thrown in some heavy diesel oil or something which doesn't thin out as much, which isn't a bad thing. Anything without a roller cam slowly eats itself unless it has certain additives and most diesel oils still have these.
Couple thoughts:
The sender or wiring may be acting up- verify the actual oil pressure with a mechanical gauge instead of relying on the vehicles instrumentation. Easiest way is to remove the sender for the gauge and install the mechanical gauge's fitting in the same location (even if just temporary under the hood), just to verify the reading.
I'd also be somewhat concerned with the lack of use no matter the level of care, since you recently acquired it. Depending on the result of the above, I'd be tempted to run some high detergency oil through it on some very short oil change intervals to flush out any gum or varnish or other solids that may have accumulated through extended storage.