Replacement twin spark coil

[Stan Palmer]

Non marque I am afraid, but this is the place with the spread of knowledge.
A friends 1983 RS 1600i has a unique ignition system by a German company AFT. One of the two 12v twin spark ignition coils is failing when hot. Attempts to buy another have failed, indeed there seems to be very little information about AFT or this system. I am presuming it is a wasted spark type, and although it is energised by an early black box, that it is basically the same as normal coil systems. I was hoping to find out what parameters to measure on the good coil, to enable matching with available twin spark coils. Or alternatively finding a company with the expertise to provide a suitable one.
The classic mechanic he normally uses has only suggested a complete new modern electronic system, which he doesn't want. It's beyond my knowledge, I can only help if I know what to measure and the seller of coils have enough knowledge to match with what they have.
Stan