From the Library section of the site, on page 53:
The short answer is that BOTH top and bottom pieces are included in a CMC kit. I don't remember ANY hardware (nuts, bolts and/or screws) included with the kit, other than those re-used from the donor car, so you'll have to supply that, but the upper and lower brackets were. You may also find that you have to "adjust" (read that, modify) the lower bracket for it to fit correctly, but that should be minor.
Gordon