Hello! I only really joined to add my input on this, even if it is about 6 years late.
I have 2 red Darth Vader helmets. One I'm 100% sure is genuine, and one which I'm less so sure about. My good one is flawless, it is identical to the final helmet; except red of course. My other one is potentially an even older prototype, it's made from a slightly less brittle plastic and lacks the number markings on the inside, apart from that it's exactly the same shape and dimensions as the final helmet. I don't think a red body was ever made as the torso brick wasn't new, just a new design.