Most piston suppliers sell '1sies' but not sure about that with the KB's and no, not a good idea to drive it. Still not sure of the broken piston piece didn't make it's way up into the intake to make ruin of other cylinders. I've seen engines where someone 'lost' a small part like a nut from an air cleaner and instead of looking for it until it was found, they just got another and well, one engine had damage in more than one hole. Also, since you have one ring gap too small, what are the other's like in the other 7 holes? Like mentioned already, that engine needs to be pulled apart to do a good checking out and I mean check everything including the springs on the heads, bearings...uh everything.