What most don't realize is how many configurations could be ordered back in the 20s and 30s, even when ordering a pump gun. Stock lengths varied as did dimensions and the early ones were often 13 3/4 but I've seen latter ones 14 1/4 (B grade checkered stock). I would agree with you that if it has the original butt, it's likely original. Often they were cut due to unpopular pitch angles designed for heads up shooting or to make them into kids guns.
The different weights of you barrels, if I had to guess, is probably due to one being honed out. These are old guns after all and often smiths needed little encouragement to hone out light pits. I suppose there is the possibility a certain barrel was requested to be struck lighter. Some might laugh but the majority of B grades I've seen have been plain barrels, not solid ribbed, so I think that's feasible even if not near as likely as it just being honed out. A bore gauge might tell the story.
Barrels are sort of all over the place, I have 26" Full choked barrel and 27 1/4" barrel marked Full that both mic out the same. The 27 1/4" barrel also weighs the same as my 27 7/8" solid rib at 1 lb 10oz. Bore diameter of the solid rib is only .003 larger. Remember though, the ribs on these barrels were machined as part of the barrel, not added on, so likely that lead to more hand work and striking. (I'm making some assumptions) These were working guns and the easiest way to go from full to Modified was a hack saw which might explain at least some of the unusual lengths. I've seen enough guns though to believe many left the factory with slightly different length barrels.
Sorry for running on!
Tim
