Was it thumping before it shut down, or only after you replaced the distributor cap & got moving again?
You can pull the distributor all the way out and check its drive gear that interfaces with the cam & check the slotted end that drives the oil pump. Just to make sure no pieces are missing/broken.Something there may not be meshing correctly. I'm not sure if the distributor could worm its way out if it was not secured or properly seated.
That stinks, man- but good call on the tow truck after hearing the thumping noise! My curiousity would have me dropping the oil pan, too.
Brad
