1968 Chevrolet El Camino Oil pump

Unless there's some engine I'm not aware of, the 350 is a very popular small block, but that is irrelevant. Remove the oil pan, then you'll see the oil pump bolted to the rear bearing cap. On the new pump you may want to insert the pickup tube with the screen down a little too far, bolt the pan on with no gasket to force the tube to turn to the correct position, remove the pan, then braze the pickup tube to the pump body. Those tubes have been known to work loose and fall out resulting in the pump sucking up air, and no oil pressure. Remove the pump to braze the tube so you're not playing with the torch near the oil on the engine surfaces.

What kind of problem are you trying to solve? Oil pumps get blamed for a lot of things they don't cause.