Leather Cuirass Lorica Musculata, I used to think no way but

[Tarbicus]

I'm not saying the whole panoply isn't based on a real panoply, just that the Emperor need only sit for the head part. A bit like when aristocrats had their portrait painted of them sitting on a horse, but they actually sat on a wooden frame for the sitting. I still maintain Augustus looks rather butch, and I wouldn't be surprised if someone else's body was used as the body model from the neck down. There isn't any actual need for the armour to be worn by anyone; it also could have been modeled by itself after initial sketches are made of it being worn by a stand-in.