Using different length barrels will "work", but not optimal. The correct barrel length will, in my opinion, let the holster "hug" the muzzle, even if it isn't formed to the muzzle, exactly. It's akin to cutting the bottoms off a pair of pants as opposed to hemming them. Both fit, but it's not the same.
... as for molds. Bunkhouse Tools has some great SA and vintage guns. Boise Foundry has odd, larger frames included in their catalog.