SilverWook said:

Those costumes have been discussed a few times before. They are real high altitude flight suits that first appeared in the Ray Harryhausen film "First Men in The Moon", a few years before they turned up on Who.

I'd love to know where their whereabouts today. Haven't spotted photos of the Bossk costume at any of the exhibitions.

It's things like this that make me think we need a 2nd Star Wars Wiki. Wookieepedia is great for in-universe, typically-EU stuff. But a 2nd wiki focused on behind the scenes, technical issues, etc....that's more what OT.com-ers would contribute to.