I've heard some interesting things about the dual exhaust ports for the single cylinders. Like you said the biggest problem is a having the single cylinder not constantly spooling the turbo. I've heard of a couple guys creating one exhaust tube twice as long as the other, to help spool, but I would imagine this would be hard to make efficient unless you have a dyno readily available to you. Check out my previous post, there is some pictures of my single cylinder turbo set up

 

That's not a problem, it's the exact opposite case. A single cylinder will outspool a four cylinder engine of the same displacement, in a common collector application.

You very much do not need a dyno to determine correct pipe lengths. That ---- varies wildly with engine rpm and temperatures, the general rule of thumb is longer reduces reversion at the expense of spool. If you still have any thought in your head that you need to get pipe length "correct" then you are a ******: the simple fact of the matter is that boost works, and it will be easy to overpower a motorcycle.

 

I would say ditch the carburetors and go with MicroSquirt!