Grigg: You are right. Mixing apples and oranges will get you any result you wish. Grade 8 from ARP would be stronger than Chinese Stainless steel from Home Depot. But the point is: 17-4PH Stainless steel is a little stronger than Gr 8 when comparing SAE type quality. BTW I am not advocating using CRES or Gr 8, just the factory recommended bolt.
DrewP: Gr8 is not stainless steel, it is a carbon steel alloy.
Fast Truck: You are the person we should be following on this because you are staying on topic and giving specific engine info. I did a little checking and found out the shoulder does locate the cap fairly acurately (for that era), as you said. They are GR 5 marked. They are listed as .056 GM part No. and the bolt uses a .060 thk lock? washer. The 056 refers to the shoulder dia. being .56 or real close to 9/16. According to those who have used the studs, the non threaded portion is .56 and the threads are 1/2". That will function the same as the shoulder. The front two nuts supplied with the ARP kit will not accept a socket? SO they say a pair of 12 point nuts are needed from ARP also.
