I would be concerned that they are designed for a specific box configuration, not for an infinite baffle installation. Q too low. Although I used to use a Uni-Q kar spkr for my HT center, and in the right box, it was about 3/4 cubic foot. so maybe?
FYI, the SP1374 is the driver from the ca. 1997 (at least that's when I bought the pair I used to have) KEF Q15 model. I believe it was also used in all of the Qx5 models of that time except the Q95c, which used a beefier driver with a cast basket.
(I know all that because I took my Q15's and Q95c's apart and took pictures of them.)
The pics also appear to have the tweeters installed. From what I remember, the tweeter grille was part of the tweeter unit, which sits atop the polepiece of the woofer. But don't quote me on that.
Very, VERY good cheap speakers. The HF dispersion is also excellent. The downside for car use is that it's hard to get a 6.5" driver up high, and they don't have the rising midrange response that IMO drivers need to sound good low in the doors. But EQ can fix that.