You can use all of the 2 1/2" brake stuff if you go to Green bearings on aftermarket axles with the LBP, or cut down and respline a set of LBP axles from a C body!
You don't have to use green bearings to go to aftermarket axles. You just have to buy the right aftermarket axles.
As far as the B body axles, they usually can't be shortened to A-body lengths because of a diameter change along the length of the axle (there's a "step"). Typically only truck axles or C-body axles can be shortened down to A-body width.
