I read somewhere that ps3 users have to search by team name in order to find xbox 360 teams, so try searching by 1970s Cowboys
Here's a screenshot of them in their alts, playing my 1950s Rams team. The alts aren't in 70s style, like the regular unis are, but they are in the 70s colors (blue, light bluish silver).
If you want the 1950s Rams, the roster's not finished, so they're on private now. I can let you know when I've finished the Roster.
