Yes, the 'rule-of-thumb' was included, but EB even admits on the vid that he usually just guesses and 'gets a feel' for the correct amount of adjustment.

He explained that he bores the chambers parallel, as is required of course to make them perpendicular with the breech-face, then pulls the barrels together close to final convergence before welding in the fore-end loop. Only minor adjustments are then needed at the muzzles during regulation.

If you follow that method, then his 'rule of thumb' measurements may work. If you keep the barrels parallel right up to the loop, and converge from there to the muzzles, stands to reason you would probably need a different set of measurements.

BTW, EB discounts the latter method because he believes the muzzles would unsolder and spring apart at some later date. With rolled sheet-metal ribs, he's probably right!