The Lowndes are chiseled and snub-nosed in a way that can only be experienced in person. It is inelegant and dated.
Just pop into the C&J store, deal with their frankly trying service, and check it out. I have a large foot, not as large as yours, and even for me they just seemed freakishly long. Elven. If you're a 12, I can't imagine them not looking like torpedoes on you. No amount of trouser can conceal that elongation.
As for the Carmina Inca last, it is a bit more spread out in the ball of the foot before the end of the toebox. But be warned, everyone likes to say this model is "roomy," but it still has an aggresively rounded taper. It's not chiseled and more sinusoidal... but still. You might experience some small toe pressure depending on whether you size up or down. I wore those earlier today; they're a fine shoe, albeit a little attention-grabbing. Still, by all accounts they're more tasteful than the C&J Lowndes.
You have been warned.
I felt the same way you did about the 348 once I got to try them on in person and I wear a 7D. How do you feel about the other popular C&J lasts, including 337 and 358?