Randy,
You say you don't think Duncan would have played center for the other teams? Let's look at that.
Let's start by arguing that currently, we think of Duncan as a power forward, and mostly for the reason that Duncan started out being officially listed as a power forward. Despite the fact that he has a midrange game, his offensive game is back-to-the-basket for significant stretches, and many argue that Duncan is really a center playing power forward even to this day. In fact, he plays more back-to-the-basket basketball than David Robinson did, and we all call David Robinson a center. So the reason we see Duncan as a power forward is because that's what we started out calling him - mostly due to the fact that David Robinson was the primary back-to-the-basket player for the Spurs in Duncan's first year.
Vancouver was the worst team in the league the year Duncan was drafted. Vancouver's team consisted of Shareef Abdur-Rahim at power forward, and Bryant Reeves at center. Do they move Abdur-Rahim to the starting small forward, bench George Lynch, and start Duncan at the 4, or do they bench Big Country, and play Duncan at the center? That's a toss-up.
Boston is next. Antoine Walker at power forward - at center, you've got Marty Conlon, Dino Radja (his last year), Frank Brickowski, Pervis Ellison, Stacey King, Steve Hamer, Brett Szabo, and Alton Lister. They acquired Travis Knight, Andrew DeClercq, and Zan Tabak for the next year. Does anyone believe that they'd have displaced Walker in favor of the other players? Not me. Chalk Duncan down as a center in Boston.
San An - a power forward because of Robinson.
Denver. Denver had Laphonso Ellis and Antonio McDyess at the big forward, Ervin Johnson at the Center. They drafted Tony Battie, a center. Chalk Duncan down as a center.
Philadelphia. They had Derrick Coleman at power forward, Michael Cage and Scott Williams at center. The next year, mid-season, they traded to get Theo Ratliff. Mark Duncan down as a center coming in to Philadelphia (they most likely wouldn't have gone after Ratliff if they had Duncan from the start of the year).
Dallas. They had nothing: Shawn Bradley, Chris Gatling, Samaki Walker, A.C. Green, Oliver Miller, and Greg Dreiling. Did they want a power forward, or a center? They played A.C. Green heavy minutes the next year, and Shawn Bradley at center. I think Duncan takes Bradley's spot. A center for Dallas.
New Jersey. Jayson Williams at power forward, moved to center the next year to allow the rookie Keith Van Horn into the line-up. If you don't have Van Horn (because you picked Duncan instead), do you move an established power forward who is 6-9 to center? I don't think so.
Toronto. They had Marcus Camby, who was projected as a forward at 6-11, 220. Duncan is 7-0, 248. Which guy plays center? Duncan, especially considering that Toronto had Sharone Wright pencilled in at center before he went down with injury.
Golden State. Joe Smith at power forward, Andrew DeClerq and Felton Spencer at center. Duncan's a center - especially considering how desperate Golden State was to find one; they drafted Adonal Foyle, a center, Marc Jackson, a center, and acquired Erick Dampier, a center, in exchange for Chris Mullin.
Milwaukee. Vin Baker at power forward, traded to Seattle, for Kemp to Cleveland, and Tyrone Hill to Milwaukee (I've got no clue as to who else). Do you make the trade if you get Duncan? Do you trade Danny Fortson for Ervin Johnson? The 1997 Bucks had Armen Gilliam and Tyrone Hill at the big forward, and Ervin Johnson at the center. I think Duncan replaces the worst scorer and rebounder - Ervin Johnson. Gilliam's minutes were slated for Tyrone Hill. But if they have Duncan, I think they keep Baker, and go with Duncan and Baker in the frontcourt - Duncan at center.
Sacramento. Olden Polynice is the center, Lawrence Funderburke, Corliss Williamson, Billy Owens, Lawrence Funderburke, and Otis Thorpe are in the front court. Polynice is 6-11, 220 vs. Duncan's 7-0, 248. Obviously, Duncan is dealing with a cast of scum, and at the time, Corliss Williamson is seen as a tweener. Complicating the situation is the fact that Sacramento's pick that year was Olivier St. Jean (Tariq Abdul-Wahad), who was seen as a 3 in Sacramento (since Mitch Richmond was at the 2), which necessitated moving Williamson to more minutes at the 4. Assuming St. Jean wasn't there, that means Corliss Williamson may stay at small forward. That leaves an open spot at power forward. So let's call Duncan a power forward here.
Indiana. Rik Smits at center, coming back from injury, at center, and Dale Davis and Antonio Davis at the big forward. Indiana's draft pick, Erick Dampier, a center, was traded to Golden State for Chris Mullin. Given no Mullin, you're looking at replacing Smits or Dale Davis. I say Indiana replaces Smits with Duncan - mostly because of the injury concern, and elevates Jalen Rose to the starting line-up at small forward. But I could see you going the other way. Call this one a toss-up.
Cleveland. Here's the most interesting one. They've got incoming center Zydrunas Ilgauskus, who missed his entire rookie year with an injury, and young center Vitaly Potapenko. They dumped somebody - I'm not exactly sure who, but I know Tyrone Hill, their starting power forward was included - for Shawn Kemp. What do you do if you get Duncan? Do you gamble on Ilgauskus, who has yet to play an NBA game? Do you trade for Kemp? Assuming the Kemp trade goes through, then it's a no-brainer - you play Duncan at center and Kemp at power forward, which begs the question of what you do with Ilgauskus and Potapenko. But do you not make the trade for Kemp, and gamble on the two rookies - Ilgauskus and Duncan? In that case, you've got Tyrone Hill, which, in my mind, makes Hill the power forward, Duncan the center, and bumps Ilgauskus to the bench, even though, in retrospect, the smart move would have been to bump Hill to the bench, start Ilgauskus at center, and Duncan - who was a center in college all four years - at power forward. Too difficult to call.
So, for the 13 lottery teams, Duncan ends up as a center for eight of them, a power forward for two (Sacramento and San An), with three of them too difficult to call.