yes and no
really depends on the gun, the part, and how perfect you want it to be.
it's little things like say a gearset as slightly more backlash in one box compared to another, might be bugger all wrong with the gears or the box just they aint a perfect fit, might well be grand for most uses (hence universal) but if you're pushing the limits then maybe not.
thinking about it that's a question that's really hard to give a straight answer to.