As far as I'm aware, .44 Winchester repeater rifles didn't come in differing lengths for different sized people!
Actually, they did.
The classic lever action rifles were offered in bewildering variety of calibers, barrel lengths, barrel types, stock lengths, finishes etc. Plus cutting the stock is just about the simplest gunsmithing operation you can do.
Fitting the gun to the shooter is a very basic thing on the civilian side. It's the army grunts (and to some extent, Hollywood extras) who have to live with whatever they are issued with.
IMHO, it would be natural for a smaller person to look for a smaller gun. This is not an era of mass produced goods. You go to the tailor, he will make a suit for
you. You go to the gunsmith, he will fit a gun for
you. Ofcourse sometimes you have to make do with what you can get, but it's not at all out of the ordinary in this era for every single thing you own to be
custom made for you.
Remember, we're talking Old West here, individuals who bring their own equipment, not government standard issue for everyone.
As for the figures: I think this is one of the genres where small variations in figures matter the least: There are no massed formations and there's even very little hand to hand combat which would require placing miniatures next to each other for easy comparison. Every figure on the table is literally an individual and usually viewed individually.