I contacted two suppliers of Delano products (since Delano itself did not reply to any email I’ve sent) and they both confirmed that I can simply swap the bass and treble pot with a 50k/50k stacked bass/treble pot. Bass-Parts from Germany sells them: Stacked Potentiometer (bass/treble) – BassParts.de

As far as I know I can simply solder the wires to this one and I’m done.