I have some 57 rearend parts taking up space in the garage:
57 Chevy rearend center section, pumpkin, gears, etc.
I have a couple center sections up for sale. These are NOT posi cases, but can be modified for posi if needed.
Fully rebuilt, 3.36, complete assembly - $250
Section with 3.55 assembly, the gears inside have some pitting, you will need to replace, or you could possibly run them if you do not mind the noise - $100
Complete 3.36 gearset, removed from housing, clean gears, spiders and carrier. - $100 (these were pulled from a running rear end when I upgrade to 3.73's)
I also have the stock drum brake setup, they were pulled when I went to discs. make an offer, sorry no pics of those.