I don't have an answer to your question, but I've got a set of headers to install and I want to know the answer.
it depends on what size header tubes you have. 1 5/8 primary tubes, you can run just about any locking bolt and be fine. some 1 3/4 primary headers have the tube so close to the bolt that you can't get a wrench...
Thanks for all the comments and help! Got the headers on yesturday, and hope to finish this weekend. All went good so far..... Hope to post pics when done.