After you get them on there, take the car for a drive to get up to temperature, and re-torque the header bolts while the motor is hot. This should ensure that they don't back out on you.
I just do it snug and another good umph to it and even after all the times ive checked theyve never came loose or had any exhaust leaks. At first i though u meant what torque spec they should be at? i forget but it doesnt matter cuz u can only get a socket and extension into like half of them.
Really!? I popped a header gasket couple weeks ago due to a missed shift, and I went through and tightend them up to see if I could get the tick to go away, and a friend of mine told me I probbly warped my headers cause I over torqed them.... I didnt give them hell, just snugged them.
So just snug them real good, run the engine and then re-snug. Cool.