Got a replacement ignition amp unit for me electronic distributor.
put it on the distributor, put same on engine, put the electronic coil on and...
...sod-all. zero sparks, just as it was before.
bugger.
so I suppose it must be the pickup bit inside the distributor that's at fault.
on the bright side, I now have a spare amp unit, so there's zero chance of that failing in future.