Years ago I had that happen on the 302 I was running at the time in my 27. Pulled out from a traffic light and started hearing ticking. Thought I blew a header gasket, but when I looked at the oil pressure gauge it was on zero. Pulled the distributor and the end of the pump driveshaft was rounded off instead of hex shaped. Put a new driveshaft in it and drove it for another few years with no problems.

Don