nick: trust me, I know about the head bolts
I was thinking, if I were in Bill'* position, i'd torque all bolts the same [the way you get it the first time], then go back and make sure it'* still the same torque. To compensate for the header getting closer to the head. As far as bolt stretch.. IMO if the stretch varies so much between the bolts to the point where it will make the header not seal properly, and you are going to worry about it.. get new bolts.
I will agree about the bolts needing retorquing after a few heat cycles.. when I pulled my headers again they weren't very tight, but i torqued them down to 50ft lbs. Felt like around 30ft lbs.. maybe 40 at most.