I have'nt made any mods on my '69 EB-3 but I've been tempted for a while. It's tricky to leave out the choke in position 3 and still have it in position 4. What is also tricky is that the resistor is connected always in series from the neck output.An easy way to try without a choke (make the neck pickup equal to an EB-0) is to disconnect the choke coil wire at lug 8 and the capacitor wire at lug 7. Also use a wire and shortcut the resistor. This way you can see if you like the unchoked sound in position 3. I'm not sure the bridge pickup will be that much drowned out because since the pickups are wired in parallell the high DC resistance of the Mudbucker will be slightly "shortcut" by the bridge pickup.
Also notice that if you want to individually adjust the volumes you must switch the connections on the volume pots. Gibson connected them so both volumes act as mastervolumes. They did for some really strange reason (which is beyond me) connect the output jack side to the mid lug of the pots.
If you can make anything out of it I made an alternative schematics from the original.
Original:
Mod:
Position 1: Full Mud
Position 2: Full Mud + bridge pup
Positon 3: Mud with resistor and capacitor + bridge pup
Position 4: Like position 3 on the original schematics
I have'nt switched the wires on the volume controls on the schematics but I would do that as well.