ive recently done the rears on my car, and ts reasonably easy to do.
personally if my front calipers were shot id just do an s13 front suspension conversion with LCA's, tie rods, tie rod ends, hubs, calipers, rotors and R31 castor rods so that u could run s13 coilovers...
but thats just me
ive been in the s12 game for many many years now so i definately know its worth it!
cheers
will