I don't have any of these guns, but I've read that the "regular" guns work fine with the Leverevolution ammo. You lose about 100 fps or so with the shorter barrel. Maybe an inch difference inn trajectory??? You'd never notice out to 200 yds. Buttstocks are pretty universal, obviously a pistol grip stock won't fit a straight stocked gun, there's no curve to the lever. Forearms are not universal, some need a fore-end cap and some use a barrel band. Big deal about the XLR? They are darn cool looking.
Longer barrel means a bit more velocity, barrel rifling is different, laminated stocks are more weatherproof than walnut, same with the stainless steel vs blued. I'm very surprised that some of the guys with the XLR haven't answered this. Hope it helps out.