For the 4.3L V6 -- there's two filters available for it; a standard length and an extended length. Which one would you go with?
My 1999 S10 4X4 owners manual lists one filter for the 4.3... AC Delco PF52
Where are you finding that listing for two filters? Who's the source? I'll bet it's not a GM source.
Many vehicles have filters with diameters that can house different sizes / brands. But those are 2nd party outreaches, outside of GM, in 2000.
BTW... the other AC Delco that fits and is shorter is the PF47. But it's not an added option inside my GM owners manual.