I don't think of Howard as long, but Prince is sort of the prototype for the sort of player we've been discussing here for a couple of years.
The need for a long 3 may be eliminated by a decision to pursue some athletic 4-types. To that end, there's a part of me that thinks that if the Spurs are to pursue a player on the Warriors' roster, Troy Murphy would be the most logical fit. That would assume, of course, that Murphy could be available, which I doubt. Dunleavy strikes me as a longer version of Brent Barry without the great stroke from behind the arc. Maggette is intriguing, but: (1) he's not really either a long 3 or an athletic 4; and (2) he's a guy who would demand the basketball a lot, which would take too many touches away from Duncan, Parker, and Ginobili. For that matter, Murphy brings the 2nd problem as well.
Again, there's a reason that Pop identified the need as a Derrick McKey-type. It's all about a defensive-minded, long, athletic player who can be efficient on the offensive end and content to be a relatively minor offensive contributor.