Pull the distributor, matchmarking it. Get a drill with the hex socket attachment on some extensions and ultra carefully lower into the block. It will slide around the oil pump driveshaft. Spin the drill and read the guage. If this fails, you pump or your pump driveshaft is crap. Luckily, if you have a magnetic attachment, it will lift the driveshaft up some so you can see it's condition. Maybe the distributor is not engaging this same shaft or it's stripped or jumping.
Just for laughs, try running the drill in reverse. Anything stuck to the pump pickup will be blown off from oil heading in the opposite direction. I cleared a fuel pump out by running it in reverse once. I bet the same will work for the oilpump.
Unless you crazy bored out the oil passages or you have no oil, I suspect the guage more than the oil system. Pull a valvecover while drilling. If oil is going everywhere, you're all set. Replace guage.
I seriously doubt total pump failure
