"a threaded hole right above where the oil filter screws in" - Off the top of my head, I would guess that it is the hole for the oil pressure sending unit.
TECHNICALY ALL OF IT CAN BE REMOVED. LEAGALY NONE OF IT CAN BE REMOVED. IT DEPENDS IN HOW STRINGENT YOUR STATES EMISSIONS LAWS ARE AND IF THEY ARE INFORCED. ALL THE EMISSIONS EQUIPMENT IN YOU RIG WERE PUT THERE TO MAKE IT COMPLIANT WITH ETHER STATE OF CALIFORNIA EMMISIONS LAWS, OR FEDERAL EMMISIONS LAWS.
I would take that to mean the equipment that cleans up the vehicles emissions is removed from the engine.
removed
The radiator drain plug on a Chevrolet Corsica is the lowest, skinniest hose on the back of the radiator. The radiator cap will have to be removed to allow for fast draining after this hose is removed.
The pan has to be removed and a new threaded nut welded on the inside of the pan. On an '88 I would just change the pan. After market pans aren't too expensive.
Egr valve is for emissions it reduces nox so will not be harmful to engine
The EVAP canister on a 1996 Chevrolet Lumina is located under the rear of the vehicle. The spare tire has to be removed to reach it.
there is the spark plug boots
the o2 sensor is for the emissions controls. It will burn moor gas and carbon the engine.
they clean the coal as it passes through with machines called 'scrubbers'
the fuel pump is inside the gas tank, the tank has to be removed and the fuel pump can be removed from the top of the tank.
You should seek the advice of the Plastic Surgeon regarding this. Thread can break. They can be removed successfully by a Surgeon experienced in thread lifting procedures