The oil pressure sending unit location on a 454 Chevy engine depends slightly on the year and specific engine configuration, but it's generally found on the
front of the engine block, near the distributor. It's usually a relatively small unit with one or two wires attached. It might be on the driver's side (left side as you're facing the engine) or very slightly angled toward the passenger side, depending on the specifics of the engine and any aftermarket modifications.
You'll need to visually inspect your engine to locate it precisely. A repair manual specific to your 454's year and model will be the most definitive resource.
