Are the K2 and K3 frames different where the belt slides through? I put a Kifaru belt on my K2 frame a few years back and it was pretty simple. I don't recall exactly but I think all it took was maybe adding some velcro to the belt. I've got a heavy duty (but not commercial) sewing machine that I would have used. My sewing skills are mediocre at best but you don't see any of it once installed. If I remember correctly you end up with an extra strap on the belt that you don't need and can just cut it off.
I've never actually seen the K3 frame and it could be different from the K2 where the belt slides through but if not, its a pretty simple install. The Kifaru belt gives the pack a plush ride and I've had no desire to upgrade since making the switch.
Good luck.
Paladin