If the original SSBC kit used stock Impala ss rear disc brakes to add to a fleetwood, then you can get loaded calipers, and rotors from Rock Auto. The loaded calipers I got from them not only had the pads, and guide pins, they also had the mounting bracket for the rear calipers. Took a couple days to get them, but I am sure they offer overnight delivery if you order them today.
1994 Chevrolet Caprice Classic Woody Wagon. (My toy)
2014 Chevrolet Silverado 2WD 2WT RCSB 4.3 ALLOY V6 (My daily)
1994 BMW 325i Cabriolet 2.5 I6 (My flip car that turned into wife's toy)
2007 Pontiac G6 VL 2.4 I4 (Wife's Daily)