Looks like the whole model was built in 3d and then milled or something... If you look at the two cannons on the side of the head, you will see that one of them is flipped! (only the lower, longer cannon. The upper, cut off cannon is not flipped)
The cannon is a part from the Tamiya Flak Vierling. That Flak had 4 cannons (vier = four). All four cannons were exactly the same part. There never was a cannon that was flipped.
That flak also supplied a lot more parts for the ATAT. The tiny rectangular vent holes, the two elongated parts for the inner ankles, some parts for the belly, and the shield on the back of the body. Even those shields were engeneered. Some of teh rivets do not line up.
Look at the long, curved detail near the "hip" of the ATAT (the broken piece in the photo above) and the round piece with the hole on the ankle: Those parts on the MR ATAT are A LOT smaller. Makes me wonder how accurate teh size of the model is.
Tim