I wanna know what you guys think is a good SQL box for this

-12 Differential Drive- Design Subwoofer
-Suggested Retail Price: $950.00
-Differential Drive- Design (DDD) motor
-Die-cast vented basket
-Kevlar--impregnated paper woofer cone
-Nitrile-butylene surround
-Power handling RMS: 700 watts
-Power handling Peak: 4,000 watts
-Cut-out diameter: 11
-Mounting depth: 10-1/4
-Dual 6-ohm voice coils
-Sensitivity: 91dB @ 2.83V/1m
-Power Handling: 700W RMS, 4,000W Peak
-Frequency Response: 18Hz ~ 1kHz
-Impedance: 3 or 12 ohms
-Voice-Coil Diameter: 3 (76mm)
-Mounting Depth: 10-1/4 (260mm)
-Overall Diameter: 12-1/4 (312mm)
-Cut-Out Diameter: 11 (280mm)
-Displacement: 0.149 ft3 (4.23 l)

Its for my friend he wants it to be 60/40

He has a mustang so he can prolly fit 3 ft^3 box
What size should it be and what should it be tuned to?