I think we can date the Russell pants fairly precisely. The red, white, and blue Russell tag was introduced in 1983, but the Cowboys had numbers on the side stripes of their pants during the early 1980s. The 'hip numbers' disappeared in 1989. Beginning in 1991, there should be an NFL shield on the front of the pants. So, unless you see evidence of a number patch or a shield, they date to 1989 or 1990.

It looks like they're gray (to go with the blue jerseys), right?