This custom was made from Marvel Legends Iron Man torso, feet, and gloves; Marvel Legends Captain America legs and arms; modified ToyBiz Vault Ultron head; Beetle shins. It was made as part of the Sinister Six Masters of Evil entry for Custom Con 7.
I made casts of either side of the Ultron head put them together with a little extra spacing to widen the head. Limb swapping on the two Marvel Legends figures was an unexpected nightmare, and did not go too well. The figure was painted with silver spray paint and Tamiya translucent blue, then gloss-coated.