SBC oil pumps are a gear type pump in an iron housing, and typically only "fail" or stop producing pressure with cavitation wear on the teeth of the gears or more commonly scarring of the housing or bottom plate. Pretty low on the list of possible causes, though. More likely is sludge restricting the pickup tube, wear in the cam bearings, or wear in the rod and main bearings. Before removing any parts, I would install an accurate mechanical gauge and verify that the pressure is indeed low ( factory spec is something like 5-8 psi minimum at hot idle) and then go from there. If you find good oil pressure, then you probably have an electrical issue, either the sending unit or the cluster. Everything else requires at least partial disassembly, and likely a rebuild. In that case, I would pull the intake and inspect for sludge. If you have a sludge issue, it may have already toasted the bearings. You can clean the engine out thoroughly (oil pan included) and install a fresh pump and see what happens, or get a short or long lock and be assured that the bearing clearances are right and go on your way. It all starts with verifying the pressure reading.