The funny thing is the Marmit AT-AT is so accurate it doens/t need upgrades. For example I had to upgrade the Gentle Giant mini-bust. There were a bit more painting improvements needed than I first thought. Here are all the changes I made: for example the red dots on the helmet were totally missing on the GG bust (not hard to add with a bit of red paint, and lots of care and patience): there is one on the front right side of the helmet (left side in the pic) just above the small gray button next to the mohawk, another red dot on the same side, but on the back, behind the ear, a small red square on the mohawk in the back, next to the red arrow, and a red dot on the middle of the left ear.
On top of the dual cannisters (the ones in the back, with hoses) I added a black dot on the silver parts, since the real screen used metal greeblies have a hole on top (they are in fact some kind of washers) - I also added a black dot on round part of the glove commpad (it also comes with a hole in the real movie suit - again a washer). Back to the helmet I added 2 small white stripes on the black greeblies next to the BOC hangers, and I also painted the small "pimple" between the "clock greeblies" in silver. On the armor there are 2 ribbed shoulder bridges connecting the front and back armour plates, and the 2 pairs of small bumps I painted silver, as they were real thumbscrews on the screen used armor.
All these were missing on the GG bust but present on the Tomy scaled helmet and the old Marmit 1:6 figure.
Screen used suit:
Stock bust - circled in red there are the inaccuracies:
My improved bust: