Wow! I get more good thoughts here on a Laverda site than on any of the Bevel Ducrappi forums. Thanks guys
Coupla comments:
1. Synching the carbs: yes, I also struggle with the lightweight steel rods in my balancer. Even when damped, I find they're not easy to work with. (And even getting the damping right - not too much, not too little - is a challenge). John, you're lucky to still have a mercury set!
So I too tend to set them by hand and ear.
2. Update the ignition system: I hear yous guys, I hear you ...

. On that:
I see Back to Classics offer a complete Silent Hektik system, but it's €475; and Stein Dinse have the Sachse at €471. The Ignitech web site doesn't list any Ducati systems, but Belt and Bevel have the box only at AU$348 (on top of which I would have to pay 20% import duties/tax, I suspect).
At the same time, I have a lead on a set of claimed low mileage, unworn carbs. But again, they're gonna cost me $500 once tax is paid.
So you can see why I'd like to be as certain as poss. as to the most likely cause of the problem