Big Block

I need some help guys.
I'm going to make a set of 180 degree race headers for a (600 h.p., 607 lbs./ft.) FE 428 CJ. and I need real facts - no guesswork.
Material is polished 304, 2" O.D. stainless steel. I believe the engine firing order is: 1,5,4,2,6,3,7,8. What is the correct cylinder location?
F/R back/right/passenger
F/L back/left/driver
and which cylinders fire at 180 degrees?
Tubing will be equal length and tuned 18 or, 16 guage. Not sure yet. Maybe you can provide some feedback on this.
Flange is 3/8" thick, and collector is 3 1/2" O.D. x 12"L
If you can help, I would be most appreciative.

Thanks,
Big Block