If you can swallow the price, Stage 8 makes the best header bolts you'll find. They have a keeper and e-ring that fastens on to each bolt to keep them from vibrating loose. They're expensive at $50 for the set, but they look good (chrome) and work even better. I haven't had to tighten a header since installed them 2 years ago on my daily driver.
If you always do what you've always done,
You'll always get what you've always got
ARP also makes a very nice set of header bolts in Stainless Steel. They have a 3/8" bolt head on them, so you can get a wrench in there on the tight ones. I use them in my car with the TRI-Ys. Also a 6 point box end wrench with a 'custom grind' is necessary.
Steve Leslie, 65 coupe in restoration. 302, toploader, A/C, disc brakes, bench seat