[68c10airstream]

Oh, i remember an almost guaranteed forgotten item. If this is an hei that has a control module inside the cap like gm hei, your distributor ground comes through the hold down bolt. Every thing needs to be shiny, bolt, hold down, neck of distributor, block where holddown touches it. I was a gm mechanic up through the ninety's and fixed many trouble code 42 (est bypass) after engine swaps and tune ups involving moving distributors around. Heres what happens, during distributor removal or timing adjustment, the body moves into a new corroded area lacking ground. I used to do a voltage drop test between the neck area that i shined up and the negative battery terminal with the truck running. If volt meter read any value (say 300 milivolt) (that's a third of a volt) i would pull the distributor, clean the base, clean hold down and the block, problem gone, I live in the salty north so it happens often. I went to gm drivability classes, set1, set2 (specialized electronic training) and loved every minute of it. Long time ago so this is memory recall. Good luck, Brian F.