Welcome along Dan
Reference photos show two round 'stubs' on the turret ring base on the Latrun version, but not on the standard AMX 13. My educated guess is that these are essentially travel stops to prevent the rear of the turret catching on the turret splash ring at full elevation. I added them using styrene rod....

The small door at the rear of the turret (spent shell ejection port?) was added next - upgrading the details as per ref shots with Evergreen styrene....

There is what appears to be a form of cradle at the leading edge of the upper section of the lower half turret - a couple of small triangles of styrene with weld seams are used. Also, the horizontal plane elevation/depression mounts on either side of the turret are just plain round prominences on the kit. There is a separate rod in the centre and to represent this, I just drilled out a hole and inserted a piece of styrene rod....

I also added a couple of PE brackets to the rear which, while included in the HB kit, need to be 'upgraded' by drilling out a small hole on each one as per the real thing....

I've also added some more Mr Surfacer to some surfaces. While the steel isn't cast, it still has a slightly rough texture on the real thing.
Gary