The model ended up being seven pieces, two tracks, the hull, commander's hatch and three piece gun and mount; more than I had hoped for. The gun affixes to a two armed mount that attaches to either side of the front periscope at the commander's position. The gun shield then attaches to the front of the gun. Assembling it is tricky, and the three pieces are best assembled together, before being mounted on the chassis. Here is a close up showing the gun and mount without the shield:
Last is an overhead view for size comparison next to a Bradley and AAV7A1. The M113 is a little beast, but an important Cold War vehicle.
I currently only have a few of them cast up, but will add them to my site as soon as I can get more of the gun mounts cast up to complete more kits.