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All new C5 replacement pumps from GM are the 04 to present style. GM parts no longer stocks new 97-03 style pumps, but they are still available in some aftermarket and rebuilt brands.
The new style pump has a lighter weight belt pulley, which yields a slight reduction in rotating mass, but I wouldn't rate that as a significant upgrade over the old style either.
I put the newer style on during my build. I don't know if it is much of an upgrade but the pump has less rotating mass since the pulley was changed. The older style was developed so that it could run two serpentine belts simultaneously. There is no reason not to use the newer design.