I am not a expert by any means and the few that I have seen were mostly long ago, but I am going to venture a guess that the W in 6W designates an original equipment version for factory installation, which differs from the common aftermarket Lyman model 6. I think that is why the 6W's go for so much.
The 6W was original equipment on some model 54 Winchesters as well as the M70 in 375 H&H with base(later) or without base(earlier).
Do some more research and if not what was original/acceptable to the Winchester 70 or 54, you may as well make a couple of bucks for yourself, unless the other makes of vintage guns charge your batteries!
