Obviously there is no tuned length.
However, other minor benefits:
1. the flow from each port of the front (1, 2-3) or rear (4-5, 6) cylinder group occurs in rotation (front - rear - front), each cylinder is not fighting gas pressure from the next cylinder in firing order - it's in the other group
2. separate outlets for each group reduce internal pressure, produce stronger pulse at the tailpipe
3. less heat soak into the engine bay vs. tube headers
4. 50 year life expectancy vs. 3-5 years for un-coated tube header
