I have personally never seen this "London Twist" on any Lefever of a higher grade than an H. To the best of my knowledge they were never cataloged on any grade but the H, though a few DS's have turned up with them, ususally also accompanied by a doll's head & cocking indicators, which they "Ain't" supposed to have either.
Do you have personal knowledge of a D or E with these barrels?

Miller/TN
I Didn't Say Everything I Said, Yogi Berra