The spark plug gap for a 1990 Chevy depends entirely on the *engine* in the vehicle. A 1990 Chevy could have had a variety of engines (V6, V8, inline-4, etc., with different displacements). The owner's manual for that specific 1990 Chevy model and engine is the only definitive source for the correct gap.
Without knowing the engine, I cannot provide you with the correct spark plug gap.
