I suggest adding three centers behind Jermaine O'Neal. One defensive specialist who can block shots and is at least average as a rebounder. He can be on a sub-Perk level on offense. One offensive specialist who can spread the floor and hit a 15-foot jumper. He should be at least mediocre in terms of team defense, but if he were above average on defense, the Celtics couldn't afford him. A D-Leaguer or undrafted rookie free agent. D-League guys include Courtney Sims and Sean Williams, while undrafted players include Michael Dunigan and Greg Smith. If you think the Celtics can only handle three centers on the roster, then combine the third category with one of the first two. Grab an unproven talent and pair him with a journeyman center with a proven track record of dependable mediocrity.