Taylor,
Is that barrel in the lower picture 1 1/8" at breech? I'm putting together something similar (and yet very different) and have almost come to the same conclusion, that the larger plate on the L&R would work better than the Chambers Ketland, which was my first choice in some ways. I also love the double throated cock option (in the right context) and think the Manton-Ashmore can probably be tweaked to be as fast or faster than the Ketland, even if it takes a little more work initially. I may have gotten lucky with my Durs Egg, but so far it has been very serviceable, so I may just take a chance on the Ashmore if you give it a favorable review.