Hi Rotog,
Love the CXs, they're not that unlike my old Moto Guzzi...(the V the the way it's supposed to be!).
I'd like to be able to give you some helpful input but I hate to admit electronics are not one of my stronger points. I know CDI boxes can be scratch built for the CX but I don't personally know anyone who has actually done it. It must only be a matter of time before someone recognizes the market and does produce a new replacement for the earlier CX? Do you think it may be worth the "peace of mind" to take your chances and find a spare (proven) unit to have on hand in case yours does fail before they're available? It would "hurt" to miss part of our already short riding season while hunting for a used box. As you probably already know, the part we need for our old bike is only available BEFORE ours fails and we start looking for a replacement.... or after you already have one!
Sorry I couldn't be of much help.
Newt.