What I ended up doing:
$ find /brickA -type f -exec md5sum "{}" + > brickA.txt
$ find /brickB -type f -exec md5sum "{}" + > brickB.txt
$ cut -c 1-32 brickA.txt > brickA_md5.txt
$ grep -v -F -f brickA_md5.txt brickB.txt > onbrickB_notonbrickA.txt
Thanks for the help everyone.
Chris Murphy