The box WILL have to be retuned as tuning is mainly a function of the port. The size of the Peavey box extends the low end of the B&C somewhat. From what I can tell with the photo of the Peavey, you can cut the port out to the bottom of the cabinet (keep same port width) and box it in with timber to a depth of 276mm (10.9"). This opens the port to minimise port noise associated with higher power and retunes it to around 38Hz. The response shows -3dB around 34Hz, with full power available, and a small hump at 40Hz. Should kick.

Cheers
Graeme