There are two "witness marks" on the LH side at the rear of the pistol (one on the slide; one on the frame) which need to be aligned before removing the slide stop. It can then be pushed out of full engagement from the right using the base of a magazine or finger pressure, and is then pulled free.
Reinstallation usually requires only that the slide be held retracted far enough for those marks to align and reinsertion of the slide stop. Just make sure that the camming opening in the barrel lines up with the slide stop opening in the frame and that the guide rod hasn't slipped down out of engagement with its little recess at the front of the barrel lug before attempting to replace the slide stop.
I happen to have the factory manual which came with my M43. I'd be happy to send you a photocopy if you'll furnish an SASE with sufficient postage. PM me if interested.
