Yeah and only 2 centers.

It was him and Wilt mainly. I think the NBA average size was like 6'5" or something. I know it's a lot shorter than it is now.
Wrong. With only 7 or 8 other teams in the league, Wilt and Russell were much more likely to play against a future hall of famer on any given night than in the post expansion era with 30 teams and 3 or 4 (or fewer) good centers.
Back, then, over half the teams in the league had a future hall of famer starting at center. In addition to Wilt and Russell, there was Walt Bellamy, Nate Thurmond, Willis Reed, and eventually Kareem. So, not only did Wilt and Russell go head to head 10 - 12 times during the regular season, they also went against another future hall of fame center in more than half their games.
Unlike when Shaq was in his prime and the second best center in the league didn't even average double digits in scoring (i.e. 2nd team All-NBA Center - 2000-01 Dikembe Mutombo 8.1 PPG, 2002-03 Ben Wallace 6.9 PPG, 2003-04 Ben Wallace 9.5 PPG, 2005-06 Ben Wallace 7.3 PPG) or in some years where they gave up trying to find a center worthy of 2nd team All-NBA and just went with a power forward instead at that spot (2001-02 2nd team All-NBA center - Dirk Nowitski). That's how void of talent the center spot was during the prime of Shaq's career. During his prime, he rarely had to play against a future hall of famer and on most nights he was guarding a guy who couldn't even score 10 points on a regular basis.
In addition to the 1960s, the period from the mid-1980s to the mid-1990s was a great time for big men. That period saw late career Kareem, early career Shaq, plus Hakeem, Ewing and David Robinson all in their primes, plus guys like Moses Malone, Robert Parish and early career Alonzo Morning.
With centers like Dwight Howard, Andrew Bynum, Greg Oden and Yao Ming (when healthy) and other decent bigs like Brook Lopez, Chris Kaman, Joakim Noah, etc. it looks like the quality of center play is once again on the upswing. I just wish the NBA would let these guys play. I love watching dominant big men play the game of basketball - especially head-to-head. The game suffers when it's giants of the paint are sitting on the bench after picking up ridiculous "touch" fouls for holding their ground and being battered by out of control guards whose main goal is to initiate contact to "draw" a foul.
BNM