I guess you meant 1000 @ 1 ohm, 650 watts it´s VERY small power, specially to that "beefy" sub wich doesn´t look bad at all, ok i´m gonna try to explain as easy as i can, small box gives you more cone control, you need good power so the sub can get really loud, big box need less power but also, they tend to get louder on low frequencies than a small box; Said that, with the power you have, i would build a big box so you can be kind of loud and get the lows nice also.
I ain´t suggesting you a big ass box, but, i would build something like 60 liters, but that´s just me, and 31 SQ means 31" of port area , for example, 10"W x 3.1"H , 6.2"H x 5.5"W , etc etc.