I sent this to snydpie, but figured it might make sense to post here too.
Why not simply say, every owner gets one of these at random.
1. Team before 1975.
2. 1975-1984
3. 1985-1994
4. 1995-2004
5. 2005-2014
The positions would still be random, and everyone would get teams from the same eras.