Brake caliper with drop spindles issue

[Damon23]

The 13200 2.5in drop spindle from western chassis that I ordered will not work with the brake caliper that I have on my truck. I measured the thickness of the rotor and they are 1in. so I ordered accordingly. The caliper bolt holes are not even close when trying to put the caliper back on. My question is will a 1in rotor work on a truck that is supposed to have 1.25in? Maybe someone down the line cheaped out and bought smaller rotors? The part number on the calipers are
K18007150 N GM and also there is a 39 L and on the far corner near one of the bolt holes is a C30. Any help would be great as the truck on jackstands with the drivers side front off. Thanks.