You have the correct armature. The difference between your armature and the one shown in the diagram is that your armature has a long, tapered shaft on the pulley end as opposed to the short, stubby, tapered shaft in the drawing. Although there is no specific documentation of this anywhere, this long, tapered shaft was probably made early in the transition from the "short" armature to the "long" armature and allowed the continued use of the earlier pulley that had a long, tapered nose and took a 1/4 X 28 attaching bolt. No doubt they had an excess of the early pulleys in inventory at the factory when the armature change occurred. Rather than throw these pulleys out, they made the armature shaft with the long, tapered front end. Once it was time to make a new run of pulleys, they changed the design of the pulley and the shaft.
This difference in the front end of the armature is not what is causing the play (movement) in your armature shaft. I would guess that the front of the shaft where the bearing rides might be worn enough so the bearing is not holding the shaft in lateral alignment. As per the diagram somebody else sent earlier in this post, is there a spacer collar in front of the bearing behind the front lock ring? Are the felt washer and wave washer in place in front of this collar? If not, and there is wear on the shaft, there is nothing to keep the shaft from moving forward and aft.
I have lots of experience rebuilding generators. If you'd like to talk by phone, send me a PM (Private Message) with your nighttime phone number and time zone. I'd be happy to try and walk you through the problem.
Good luck. Bob Bader
