There is often an misconception that it's the length that's the key to what rpm it will make power, it's volume and area's of the pipe that will give you the length. But sure, the last fine tuning is done with different length.
I might have an onroad manifold I could measure, but that's a Hipex manifold.
Picco 2046 pipe (the new in-line) might be a good candidate regarding pipes. I guess Neal could have tested that one.
http://www.absolutehobbyz.com/RC-Con..._p_505098.html