Russell was 6'9". Besides I would argue that rebounding is more about positioning, athleticism, and hustling than it is about height.
Because Wilt was a once-in-a-lifetime athlete should take nothing away from how great of a rebounder he was. The whole era debate is legitimate, but you have to put it in perspective from both sides. Russell and Chamberlain didn't have the equipment, training, nutrition, or 30-40 years of coaching and sports technology development to help them either.
I found 25 guys 6'8" or taller in 1960. What's more, there were only 8 teams.
(http://www.basketball-reference.com/leagues/NBA_1960.html)
Once I scored a basket that still makes me laugh.