Need help identifying rear brake calipers
 

I just bought a 79 wodebody. I am in the process of overhauling the brakes. I was successful finding, and matching the front brakes. The rear on the other hand...
I ordered the front and rears from ********. The rears I received look similar, but have smaller pistons, and the brake line attaches in the side. My current calipers have the brake line that attaches to the back. Anyone know what I should be looking for?http://forums.pelicanparts.com/uploa...1388532743.jpg
http://forums.pelicanparts.com/uploa...1388532757.jpg
http://forums.pelicanparts.com/uploa...1388532779.jpg

front M caliper, 3" mounts 42mm pistons, this should not be on an SC

painted front A caliper 42mm pistons, correct for the front of an SC(except for the paint)
http://forums.pelicanparts.com/uploa...1388532743.jpg

a rear M for an SC will have 3" mounts like the first one above but will have 38mm pistons, the feed shoul be on the side not center

this is a correct rear M for an SC

http://forums.pelicanparts.com/uploa...1388533950.jpg
http://forums.pelicanparts.com/uploa...1388533987.jpg

All of the pics I posted were for the rear.. What should this caliper be on?

This looks like a front A, but to determine for sure measure the distance between the mounting hole centers, all 3" are SC/Carrera rear M or an earlier front M, big 48mm pistons is front only, smaller 38mm pistons is rear only, 42mm pistons is for '84-89 wide M rear, if the on center mount spacing is 3.5" it's a front A which will have 48mm pistons
http://forums.pelicanparts.com/uploa...1388532743.jpg

It is 3" from the center of each hole.. So I have carrera rear brakes?

3" mounts means one of the following
w/ 48mm pistons M front
w/42mm pistons 3.2 Carrera rear '84-89
w/ 38mm pistons '69-83 911 rear

note above I posted some erroneous specs, all fronts whether M, S or A are 48mm, rears are either 42 or 38 depending on year

full documentation here on my web page

Yes, it appears that the rear calipers you had are the Carrera rears for 84 to 88 with 42mm pistons; these should be matched with the thicker rear rotors.
It is tricky trying to identify calipers from the front; a rear shot showing the fluid inlet and mount spacing is far more useful. This is the A caliper with 3.5" mount spacing where the fluid inlet is on the bottom; there are two varieties for the 20mm and 24mm (Carrera) rotors.
http://forums.pelicanparts.com/uploa...1388584842.jpg
This is the M front caliper with 3" mount spacing where the fluid inlet is on the back; there are several varieties all with 48mm pistons for 911, 912 & 914/6 some with a spacer for vented rotors, some without spacer for solid rotors on 912 and 911T. Then there are the 42mm piston versions for the 914/4.
http://forums.pelicanparts.com/uploa...1388585477.jpg

I bet I had the front carrera calipers also! They looked the same as the ones I just put on. I guess the carrera calipers were just a tad wider and had bigger pistons... Oh well, I already turned them in for a core. The previous owner included new slotted rotors(for an SC I assume). Can I not use the SC rotors with the carrera calipers?

Not safely
3.2 Carrera rotors new are 24mm minimum spec is 22.6mm
older 911 rotors are 20mm new

Yes, you can use the narrower rotors, but the pistons are extended a bit. You would probably need to replace the pads when they are only half worn to ensure the pistons do not get overextended. I agree with Bill that it is not the safest solution. You want to use a proven system, not a jumble of mismatched parts; the brakes are far too important to mess around with them.