What's rare about it?
I was thinking about my yellowed white '73. The only original parts on it are the carcass, bridge/tailpiece, TRC and jack plate. Everything else had to be replaced, including the truss rods. Still a wonderful bass by the way. So I'm not concerned with originality here. I'll have to source a white Plexi TRC and that could be a problem. Click to enlarge...
Nothing rare. Just another late 70's 4001. If the white plastic is original to the bass, it's very unusual, but I don't see how the seller can prove it unless he has some sort of documentation.