disconnect the wire that goes to the actual starter motor but leave the wire connected to the bendix. This way it will kick-out but will not spin. If you are doing all of this to get rid of the starter shim problem, you are working way too hard.
Does the starter make a funny noise when you engage or let off? To make the kind of damage you showed it should be. Trial and error the shims until you get it right. The test I was talking about earlier depends on if the wining noise is as it engages or disengages. If it is when it engages you put them in either the front or the back, and reverse for the other (cannot remember which one). However, I remember I read it in the instructions for the starter when I installed mine. When you go to buy the shims, ask the counter guy to let you check in one of the starter boxes to see that the slip says. (If you are super lucky, they may know the answer). Feeler gages should not be necessary.