I took the JVC headphones appart using a screwdriver and a hack saw. All you need to keep is the drivers, cable (unless you're making your own) and the foam ear pads. This might be a good point to label the cable - left and right - if you need to know which is which.
Cut and file the plastic surrounding the speakers untill they fit into the ear cups on the vintage headphones. Cut the plastic protective plate off the back in order to access the soldered on wires and de solder from the speaker.
Strip the old speakers out of the vintage headphones. The ones in these were held in with screws. The Bakelite ear cups screw on and off so its easy to get to the speakers. At this point I drilled cable entry holes into the bottoms of the ear cups. As i recal these were 4.5mm. You need to make sure you file the hole well to avoid burs slicing the cable when it goes in.
I cleaned the aluminium on the vintage headphones with wet and dry paper and lots of water, then metal polish. Not really necessary and sometimes I wonder if I shold have, but these were really dirty and I didnt fancy wearing them as they were. I do kind of miss the patina though.