Follow the suggestions you got so far first. If you still have problems pull the distributor and check for excessive lateral movement in the shaft. Check the drive gear. Both that it is tightly pinned to the shaft and the teeth are in good shape.
Chuck
I once had a similar problem with random spark, I inspected my distributor and did find a loose drive gear
...click... Picked up a new distributor at NAPA (They had on the shelf) and no further problems
235, pertronix
Good Luck
