the cables are really a fun thing to work on. I have seen 2 different systems on the urraco (maybe one was already modified, but who knows, one had a tensioner, the other didn't):
Anyways I have replaced my cables with new ones and followed that sketch here (see pic). the tricky part is to roll the cable onto the pulley, but when you let loose it jumps right off again, therefore I used a piece of wood with bolts in it that clamped the cable so I could put it in place. then I let it loose. and everything was fine.
I also added 2 relais on the motor which makes the mechanism as fast as on a modern car....