Yep, thats the actuator I used as well. Put it on the inside of the door, and it juuuust barely will fit between the switch unit (that you outlined) and the little lifter pin for the lock. You'll be amazed when you see how good the fit is! The bottom of the actuator will literally sit on top of the casing of the existing switch box...I then drilled one small hole (I think.....) and used one existing hole, and screwed it in place. I then devised a way to implement it into the existing locking mechanism. I'd show pics, but I'd have to take my door panel off, and I'm not willing to do that.

Edit: Now that I just realized you have a W123....I am not sure if the doors are the same inside, the W123 door might be smaller and not have enough room....in which case alternate engineering will have to be devised. I've never tried it on a W123.....

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