External tooth star washers is correct. You should see "bite marks" from the washers on the pan. I am 99.9 % positive there wasn't a manufacturer call out on these bolts OR header bolts. There was NO reason. 10,000 grade 5 1/4-20 x1" bolts "could be " from more than one supplier especially if "a couple thousand" were in stock and the rest were ordered or "staged delivery". Again SAI-Buddy Bar-Cyclone etc did not function like FoMoCo. where each bolt had it's own spec and blueprint!
Randy