following this- the most terrifying part of the whole enterprise and the part which could bin the entire project-
Modifying the bakelite driver-housings themselves to accept the new Sennheiser drivers.
These bakelite housing being made up of three parts- an unscrewable telephone style earpiece and a front & rear section held together by three bolts.
Having removed the balanced-armature "mechanism" a lot of headscratching went into how to best add the new drivers to the old shape. Would it be best to mount the drivers themselves, removed from their front grille, or with their front grille still attached. Would it be best to attempt to Dremel out the rear of the driver-housings to fit the depth of the new drivers to mounthem with no external modification to the front section, of remove the front section of the housing themselves to accomdate the grille?
In the end it was decided to confront what must be done head on. After all if the front section was damaged, things would be tricky but hideable behind the earpiece, if the rear sections which also attach to the headband and cable were damaged- game over! The Sennheiser driver's and grilles had a combined diametre of 39mm. A 38mm hole cutter was obtained...