It's gonna depend on your body and drivetrain configuration. 4wd vs2wd. ext cab vs reg cab. They have different drive shafts. Look at napa.com and each ujoint lists the size specifications. Look up your truck model then look up a c2500 light duty with 14 bolt s/f. Or, best bet is to bring the 14 bolt ujoint and your stock one to the parts store with you and figure it out. If the center section of the ujoints have the same diameter you might be able to swap caps.
I had same problem on my swap. Measure the size of the caps you need and width of the U-joint cap-to-cap, both directions. Take those dimensions to oreily or napa or wherever. They should have a book with U-joint dimensions, cap sizes, etc. Whatever u-joint fits those dimensions is the one you'll need. Keep the box or at least the part with the number on it so you wont have to do all that again when you break it. Keep it in the glovebox.