Well, in stock form, the C body 73+ C body spindles are taller in overall height, which changes geometry, the axle stub is 5/8 higher in the forging so they provide a drop in ride height, and they utilize a thicker disc rotor so they can be a better heat sink, and the 73 year only utilizes the same upper ball joint as ABE bodies.
Down side is the lower ball joint mounts are not the same width, so milling the mounting holes would be required to bolt up to the standard BE joint. The thicker disc would require a change to C body calipers, or a step up to any number of aftermarket units that can utilize the thicker disc, and the 74-78 years use a larger upper ball joint that would require a new or modified set of upper control arms.
I thought the general consensus about the widely available 2" drop spindles were that their casting were a reasonable street car piece unlike the Fatman Fab units that were a welded plate.
I worked with Firm Feel about 10 years ago on a C body knuckle conversion for B body cars. I had several sets of '73 C body knuckles modified so they would bolt on to a B body lower ball joint. I also designed a brake kit that worked with 17x8 Ford rims. Firm Feel was going to build me a set of custom upper arms so I could test drive the setup on my Coronet but they had some other stuff going on and the project never got off the ground. It might have been a cool project, might have been a dud. Who knows.
