>>7579313Its actually quite a simple modification for the circle. That's a M.S.G. Heavy Weapon Unit MH13 Grind Circle affixed to the slots that would normally hold the two guns attached to its face.
A lot of custom built hexa gear forms use modeling support goods and frame arms parts, which can make distinguishing how they're constructed extremely hard, especially when repainted. Basically you just have to try and figure out the base kit they used and then pick out the individual pieces by looking at MSG and Frame arms.