180* headers on a flat plane crank should sound closer to a normal V8, as it will cancel out the effects of the flat plane exhaust pulse and scavaging effect. The purpose of 180* headers is to produce the effects of a flat plane crank on a 90-180-90 cross plane engine like the original LS crank. So it should sound great with the new crank and firing order, without special 180* headers! It will be a cool engine when complete. Did you have to get a custom cam?