I don't know what the capacity is of the radiator from B&B.
The 77-78 Mustang II radiators have the brackets and support structure to mount to the B&B front clip. They are also narrow enough to fit inside the body.
US Radiator has a Mustang II radiator that will bolt right up to the B&B brackets and with the bottom outlet pointed up so it can be routed above the frame member. HP. Part # 53160.
http://www.usradiator.com/catalog.htm
Get the 3 pass desert cool model. I have a 460@520HP with a single 2300 CFM 16" fan. Never operates above 190degrees. Make sure you duct the air to the radiator and have a fan shroud.