The 302 has the same distributor drive as all the GMC straight sixes and the Chevy 216/235 engines. It is driven by a gear off the cam. The distributor drives the oil pump. The distributor kind of floats in the hole, and if it pops up too high it disengages from the gear and the oil pump.
You could have sheared off the roll pin to the distributor gear, or the cam gear could have broken.
The 302 has a gear driven camshaft, and the gears are aluminum. It is really unlikely that those broke.
www.oldgmctrucks.com is a good GMC info site.
