Toad,
I ain`t no pro with norvels, but I have played with some using tuned pipes. I would suggest to you that it may not be worth the effort- the ame always seemed to have too big transfer ports <fuel ports/ whatever you want to call them> to me when I was trying various mods to the timing. I bet the norvel guys tried different setups when making the engine, and its the way it is because that ran best. But as you say, it is a difficult job to get right.
On another note, I found that there was a definate tuning limit when running pipes with the anodised <dark coloured> cylinders I think because of heat transfer problems. I had a quite a radical engine that was o.k on 15% fuel and the pipe, but when I tried 25% <castor/synthetic oil> the piston overheated and exceeded the max temp of the oil, and suddenly the engine was doing about 35K with no lubrication in the bore.[X(] it slowed down really fast ast the nickel plating wore off the piston.

J.M