Spindle/Rotor issue

[Dagreat7]

Hello everyone. New poster here. Been searching on here for a while now.

But i have a few questions. My mom bought a 1983 C10 a few months ago. And she gave up on working on it. I have taken over the project recently. I started to take rebuild the complete suspension.

Lowering the truck with a 2 1/2 front and 4 rear. She bought the drop kit from LMC. Not a big fan of lmc but not to bad for smaller things.

My issue is the new spindles came in with only a 4 inch axle shaft. The old spindles have a casting of K10. Makes me thing the truck might be a K10. The specs on the old Spindles are 41/2 inch axle shaft. 1 3/8 inch inner bearing size. Those are my 2 issues. The new spindles are 4 inch axle shaft, and only 1 1/4 inch inner bearing size. Rotors are 1 1/4 wide rotors and 11 3/4 inch length rotors. Outer bearing fits on both just fine tho.

What makes a C10 and a K10?
Changing rotors solve the problem? To a 1 1/4 inch inner bearing size? And a smaller rotor to fit the 4inch axle shaft? If thats the fix? What rotor is the one to use? Part # or link appreciated.

Thank You for ur help. Will keep in touch with the progress.