As a side note: I guess this was done to spread the torque out?
Quite correct.
The formula for tube length asks at what specific RPM do you want maximum power.
For a race Engine NASCAR for example, the Engine is built specifically to one particular RPM.
For a road going Vehicle, a broad spread of power is required.
Variable pipe length assists in this.
The Brute pipe for example is well known for it's power delivery, yet the tube length varies considerably.
Green is the rear cylinder pipe, red the front.
Re "original design" when I first looked at developing a Header for the Rocket I looked at was currently available.
Personally, I think that the Brute pipe really captures the essence of the Rocket.
But I was not just going to just copy that style, that's pretty "tacky" as far as I'm concerned, any one can just copy another (Didn't the Japanese do this in the 70's ?)
So I developed my own style addressing some of the issues that were current, heat on the Riders leg for example.
It's all very well being "the fastest Kid on the Block" but if you can't sustain riding for long periods of time what is the point.
Remember "It's not how fast you go along, it's how long you go fast"