SweetBMXRider, those look like single piston rear calipers from those cars if I'm not mistaken, not front calipers.
Youngmattg, from the research I've done and talking to f body guys at shows about these options, having an LT car and upgrading brakes require either swapping spindles or using a C5 conversion bracket. From what I've heard, the LS F body and C5 calipers are interchangeable, however, if you have an LS spindle, you can only run 12" rotor with either caliper, the C5 conversion bracket allows you to run a 13" rotor which can also use either caliper.
As for the difference between the LS and C5 calipers, the C5's have cooling fins that run the length of the caliper while the LS's only have fins on the back. C5 calipers are pressure cast while the LS's are gravity cast making the C5's stronger and less likely to spread. I believe the LS's have two 53mm pistons while the C5's have two 50mm pistons. From what guys have told me, you'll barely notice a difference in stopping distance between the two but the C5's will dissipate more heat and won't fade as much/fast under spirited driving.
Here are some links with more info
C5 Zo6 brakes V.S. LS1 brakes - LS1TECH
Pic of Corvette conversion kit from 6litereater - LS1TECH
IMO, I would go with the C5 bracket to get that 13" rotor, that's 2" larger than our LT rotor and I believe C5 rotors are directionally vented, but even if they're not, that extra 2" will dissipate a good amount of heat. As far as calipers, you're more likely to come across an LS caliper in the junk yard or being parted out (98-02 v6 calipers are the same), if you can get them on the cheap, go for it. If you're buying new hardware, price it out, but from the shopping I've done C5 calipers aren't that expensive new and I can't see them being much more than new LS calipers, I'd say those cooling fins would net you being performance keeping everything cool rather than the 3mm larger pistons on the LS's
As far as rear brakes go, I'm not touching mine. The fronts do all the work, the rears are just there for stabilization and having a brake bias too much to the rear can make the car squirrely.