Tom,
With the software, to design 2 stroke pipes, the only measurements that change going from twin to single pipe was the dimension of the stinger (exiting small pipe). All the other measurements stay exactly the same.
My idea to get one of the formed pipes Kawasaki's use and chop off the silencer portion. Increase the final exit tube from (should be 19mm) to the single pipe setup of 21.5mm. For the silencer any two stroke silencer from even a motorcycle (repack-able) slapped on the end to save the ears.
Yes save the weight. Twins are a lot of weight. One pipe does the same thing as twins with the exception of wide band tuning each cylinder. All the modern sleds come with single pipes, every ask yourself why.
The Kawasaki motors will turn 9k or even 10k and make more power at higher rpms (piston port rules). The higher you go up, the shorter the lifespan the more narrow the power band.
The tune on the ltd pipe is for 8300 rpm. Yes you can use one ltd pipe and all that needs changed is the exit port pipe. I have not cut one open yet but I will bet there is a stinger pipe shoved up into the forcing cone and that the diameter is 19mm. Cut that one out, weld up a 21.5mm pipe the same length as the one you pull out and weld it into place. Run your motor out to 8300. Of course use a grinder and open the transfer ports what you can. Do you need a picture of Aaen ported regular invader cylinders? Lastly shave your head down. At the moment, best information, a 440 motor can manage 14.1:1 static compression with pump premium fuel. No detonation... Beyond that race fuel >octane required.