Have you run those speakers through WinISD? If you're looking for a flat response curve (which I'm assuming if you're going for SQ), that seems like it may not be a big enough enclosure for those three subs. I personally haven't done so, but usually for accurate response in a sealed box with accurate low end you need quite a bit of enclosure volume.
Here's the thing. JLs specs are geared more towards a compromise in sound that trends towards output, because that's what most people are looking for. WinISD is a computer program that you can use online for free. You plug in the mechanical specs of the woofer (available online) and it displays a graph of the response curve that the speaker will make given a certain box volume. If you're looking for sq, you want as linear (flat) of a response curve as possible. Peaks in the curve means boomy sounds at those frequencies and you are looking for faithful sound reproduction. For example, I am prepping my custom sq install now. The JL 10w7 that I just purchased calls for a 1.25 cubic foot sealed box, as per JL. WinISD gives an optimal flat response curve at a sealed box size of 2.2 cubic feet. Sealed woofers tend to roll off in volume at a higher frequency. More enclosure volume levels out the low end. I'll see if I can throw those specs into it for you and see what it spits out.
Here's the thing. JLs specs are geared more towards a compromise in sound that trends towards output, because that's what most people are looking for. WinISD is a computer program that you can use online for free. You plug in the mechanical specs of the woofer (available online) and it displays a graph of the response curve that the speaker will make given a certain box volume. If you're looking for sq, you want as linear (flat) of a response curve as possible. Peaks in the curve means boomy sounds at those frequencies and you are looking for faithful sound reproduction. For example, I am prepping my custom sq install now. The JL 10w7 that I just purchased calls for a 1.25 cubic foot sealed box, as per JL. WinISD gives an optimal flat response curve at a sealed box size of 2.2 cubic feet. Sealed woofers tend to roll off in volume at a higher frequency. More enclosure volume levels out the low end. I'll see if I can throw those specs into it for you and see what it spits out.
So I ran both your specs and the optimum size through WinISD. The graphs are actually somewhat close, but the 1.2 cubic feet per sub from JL produces a more pronounced output drop off at a higher frequency than the optimum spec'd by the software. Either way, you're hitting -3db loss at around 50-60hz, which is somewhat high. Depending on the amount of cabin gain you get, that could be a bit peakier towards the mid-bass region than is optimal for sq competition. With proper eq adjustment that can be ironed out, and the size of the box that WinISD calls for is about 50% bigger than what you're looking at doing. It's not going to sound bad, it's just going to take more work in the tuning department.
Is there a particular reason you are going with those woofers?
Selling them and buying, say, 2 10w6s would give you a far flatter response curve, and more faithfully reproduced bass.