If it's gonna be stock and you're ok with leaving 20-40 ft lbs in the table, pretty much everywhere across the power range, then any old stock manifolds will do. Yeah the 340 mans probably make a bit more than the others.
The cheap hedman headers are total garbage. The cheap summit branded headers are actually pretty nice with thick 3/8 flanges. Get those.
Don't waste time with any kind of shorty headers they are barely better than manifolds.
Headers help regardless of displacement.