/6 sitting up for several years what to do

The cranks changed from '67 to '68. The convertor hole in the end went from a small diameter to a large diameter. You'll need a bushing or different convertor to convert depending on which way you're going. Coolant in the oil pan is never a good sign but on a slant 6 it almost always means a rod is thrown through the cylinder wall. Could be a sucked valve that broke the cylinder head but I'd bet on the rod. I'm surprised it didn't come out through the side of the block. Usually it's the #6 rod that decides to leave home. I've seen a couple of slant 6 cars that threw that rod and broke the starter ear right off the auto trans too. Killed two birds with one stone!