If you are going to do this stuff, start with the Nourish engine, you will be buying the results of years of Dave Nourish's customers' pain. The staggered crank has been done a few times here in Australia. Some of our guys love heros, and Phil Irving was one of them. The staggered crank works, but y ou instantly have the problem of losing the interchangeability of camshafts when you are developing the motor to go faster . Balance of the crank is never a problem, you just have to choose what revs you intend to pull when you build the motor, and understand that if it is going to develop a lot of mid to top end, you will have to tolerate the low revs shakes. My own bike vibrates like hell while I'm waiting behind the pit gate, but once on the circuit - up an going, it's an absolute delight. The balance factor is only 72% because that is all I could get it up to after tapping and plugging the hole in the bob weight, and judiciously drilling holes in the other side.
About the Phil Irving thing. One of our guys has completely redesigned the Vincent engine, built a bike with modern suspension with the 1400cc engine, and calls it the 'Irving Vincent' - it is a world beater. Also in 'Tuning for Speed' Phil Irving says the if an alcohol fuelled engine is rich it still makes good horsepower, so the guys have interpreted this as 'Phil Irving says you should run alcohol fuelled engine rich'. They miss the point that alcohol hides up tuning errors, and is just as difficult to get right as petrol. In fact years ago when people like Jack Ahearn and Ken Kavanaugh were racing in Europe they'd had experience with fast racing in Australia because of the alcohol fuels. But the sad fact was that the Poms could always get their manx nortons going as fast as ours just using petrol.
When I built the Seeley, I bought two 34mm MK2 Amals with the alcohol kit. I tapered the ports similar to an aermacchi 350. The needles and jets supplied from the UK were really stupid. I simply fitted the leanest mikuni needles ( I think 6DP6), and made my own needle jets from brass hex. I selected a number drill which gave about 0.117 inch hole (Triumph experience) . Riding the bike around the twisty stuff on Winton I dropped the needles until the motor coughed on gear changes around the twisty stuff then raised them one notch. I'm using the old Triumph main jets of about 650 amal size. Around our 3Km circuit , the bike is excellent, it is still a bit rich on the mains, but you can cop that with methanol. It goes like buggery ! The leaner you can get the carburettor settings without destruction, the better. The motor will go fastest just before it blows up.
We use this stuff on our Kawasaki two stroke sidecars my brother races, and it is a real hoot. We've almost come to blows arguing about jetting for alcohol. I will link you to a video of him racing, but he won't allow me to upload the one where the 750 two stroke jumped into the back of another sidecar outfit and flipped three times.http://www.youtube.com/watch?v=HYnXEQ0Aw1I