As I recall from the L C Smith Plans & Specifications book their bbls converege at approximately .011" per Inch. I checked several of my Lefevers some years back & they had near identical convergence to the Smith specs.
Much harder for me to understand is how a set of 28ga & .410" bbls could both be built to the same frame, both touch at the muzzles & Both hit point of aim. The convergence would be much greater on the .410.

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