Aidan , its the HT arcing between cap and rota thats wrecked them , nothing to do with the electronics, or coils .......... its the gap !!!
the spring has to contact the cap brush , no gaps..
on the replacement bend the spring upwards so it has to be loaded against the cap brush.. get that sorted change the plugs and then think about
deeper routed components
you can set leccy static with a bulb same as with points ,, small pea bulb from coil neg to earth , turn engine slowly and with ign on the bulb will light as soon as its triggered by impulse or mech points both do the same . check the pulley marks as soon as No1 is approaching TDC you want around 8-10deg btdc.
Pete