I would think that on size alone it would fit and mount in. Depending on which of the engines the 1985 Celebrity had you might need to make a number of modifications to use the Corsica engine in the Celebrity. The two engines are NOT identical.
The engine codes for gasoline engines in the 1985 Chevy Celebrity: 2.5L 4 cylinder engine code R 2.8L V6 mpfi code w 2.8L V6 carburettor code x
Which engine does your 1985 Chevy Celebrity have? The two engines are very different.
The oil pump on a 1985 Chevy Celebrity V6 is bolted to the rear main cap.
oil pan
Follow the top radiator hose down to the water outlet on the engine; the stat is in there.
Will the transmission from a 1985 Chevy Celebrity fit a 1991 Buick LeSabre
The pcv is located on either valve cover or the intake.
If your car has the 2.5L 4 cylinder engine the gap is 0.060" If your car has the 2.8L V6 engine the gap is 0.045".
Try cleaning them.
Built into the alternator.
Looking over the passenger fender it is alongside the valve cover at the top of the engine.
If your engine has a carburetor the filter is in the supply line into the carburetor. If your engine is fuel injected the filter is right next to the gas tank in the fuel line.