What is the point of discussions about balance and weight and handling if you're just going to put a strap on the thing and louse that all up?
Sounds like a good idea for Rocketman - does mounting a sling change the gun's MOI? I don't think so, since it's mounted on two points, which seems to be equally remote from the points of balance, and it doesn't weith that much.
But then again, where I grew up, if a shotgun didn't have sling swivels it was taken to a gunsmith to be fitted with them, which might be coloring my judgment...