Absolutely, 100% not factory-built. The ad states it is a Bauer conversion. Very stinkin' awesome, though, with a decent price, too.
$26,900 is NOT gonna get you "squeaky clean" on this type of conversion/customization...$50K will, though. If you've seen what regular cab or Club Cab '89 - '93 Dodge Cummins trucks, whether 4x2 or 4x4, are selling for right now, you'd change your mind. I think this is a LOT of truck for the money. I know a place about 30 minutes North of me that does this to Ford trucks every day, and their price is right at $50K...PLUS the cost of the truck!
Chances are probably 98%, this is not a recent job, as this has rust in the rockers, and it is a Minnesota truck. If I were a serious buyer on this, I'd pay to have a PPI done on the truck, accompanied by between 150 - 200 photos or every conceivable area.
Looks like the builder took a 1986-earlier factory Crew Cab and added a Club Cab section from the rear doors, back. 1992 doghouse and grille, bed assembly plus trim and tailgate, plus drivetrain. Extended either a 1993 Club frame or an earlier Crew Cab frame.