2X to what Jay said about weight. Already had Baer's 13.6 rotors with the PBR's on the front of my '70 Stang. Aluminum hat, bolt-on lightweight steel rotors, 16" wheels required. A really light and great stopping set-up.
Then, I got SSBC's 9" Ford rear kit with the parking brake . Calipers are off a Lincoln IIRC. Rotors and calipers (steel one-piece) weighed a TON! Sorry for some years now I didn't return same and get Baer's lightweight rear disc kit as well but it was about $200 more.
Live and learn as I could have saved an easy 40 lbs. of unsprung weight off the back end. That said, unless you really need your ride to lose weight, the cheaper SSBC kit does work fine.