Re: exhaust what do you think?
IF the single muffler was restrictive, then some of the exhaust gasses will look for the path of lesser resistance and flow through the top muffler which will give you a bit more top end (again assuming that the exhaust was a bottleneck for "breathing").
I don't think it will be any quieter, COULD end up being louder. I don't expect you'd lose ANY low end torque....unless the single muffer was SO restrictive that it wasn't flowing enough even at low revs.
Two stroke exhausts are SO important to how the engine operates (eg - backpressure, scavenging, harmonics....), that just about anything can happen when you start messing with pipe lengths and mufflers, etc...
Give it a try and post your results back here....should be an interesting experiment!