Really good question. Red was always the best in the game at acquiring just the players a team needed to get over the title hump. Havlicek kept the 60's dynasty going, Paul Silas made the 70's group into a title team, Parrish and McHale were brought in to get us past the 76ers who had too much size for us in the 1980's ECF. Then we traded for Dennis Johnson '84 when we needed a little new blood and a big, defensive stopper in the backcourt - plus he had the perfect mentality to be a Celtic.
For me, this team needs three players to start winning titles - a playmaking point guard, a tough power forward who has an inside scoring game and a knock-down shooter. We need more than one addition. Those three coming off the bench to replace the current group that gets minimum minutes are what we need. We are too dependent on the first 8 and Ime is playing the starters into the ground.
Pritchard could develop into the shooter, but he is not at the level of prime Kyle Korver or JJ Reddick.
Horford is our current power forward, but is aging and does not bring the physicality we need to add inside.
A playmaking point guard is a desperate need and could be a starter.
Marcus Smart has 6th Man of the Year written all over him - if he was willing to accept the role.
A couple months ago I would have been fully on board with at least two out of the three needs. And, there's no doubt in my mind that we still need a long-term replacement for Al (I don't think it's Grant Williams), and we need another shooter. But really, to be contenders next season, I think all we really need is that shooter who can do a few other things. A pure offense, no defense shooter won't get run with Ime. As for PG, between Marcus and White, they can handle things.
To me, as I've mentioned, the guy is Harrison Barnes. He checks every box:
1. He can start at PF or play SF off the bench;
2. He's an excellent shooter;
3. He's on a reasonable contract;
4. He brings legit scoring punch;
5. He's decent as a rebounder and a passer
Timelord / Theis
Horford / Grant
Tatum / Barnes
Brown / White
Marcus / Pritchard
or, going small:
Timelord
Barnes
Tatum
Brown
Marcus
or, pure shooting:
Horford
Barnes
Tatum
Brown
Pritchard
The tricky part is obtaining him. As discussed in another thread, it would be a two step process, where we acquire a player (preferably an expiring contract) into our trade exception, and then flip that player with a #1 for Barnes sometime later.
I do like the Otto Porter suggestion above if we wanted to be more cost-conscious, but this close to a championship I'd go all-in getting a guy who could help us the next four years or so.