You guys can laugh if you want to and say you don't believe me but ...........
Here is a poor mans locking system that works every time. I've done this over many years with great results.
I put my combo together during the Christmas holidays in 2002 and have not lost a single header bolt and I'm still using the same Felpro gasket.
All I did was tighten them after two heat cycles.
Its all been good since then.
The pic shows a regular lock washer on the left and the middle washer is the what I've used the most but if you've got a bolt that is really tight, you can use the star washer you see on the right.
Later
Grady