Torque specs for a 77Z header?

Good morning, after searching I still do not have an answer. I am switching from the stock exhaust manifold to the 3 to 2 no smog headers on a stock 77 280Z.

I switched to all studs ( 10 mm studs at # 1 and 6)and need the following info please:

1. What is the torque specs to tighten down the nuts.

2.Is it a good idea to use two gaskets( the metal in between ones)when installing? I will be adding copper permatex to both the block side and header.

3.Proper tightening sequence is from the center to the outside right, or it does not matter with headers?

Thanks,

I am posting these questions on Zcar also, I need to get this done today.

THANKS

-Rick