Yeah I thought about doing C clamps, but I didn't have any big enough, and since I already had the quick clamps they worked well enough.
I didn't split any rivets, although some of them folded over kind of weird and look pretty ugly. Considering the primitive flaring device (a screw head) I was using, I'm actually surprised they look as good as they do.
I found out that there's a Tandy Leather close by, so I picked up some proper setting tools today, and we'll see if my eyelets get better on the next attempt.
The retention on all three is pretty good now. The S5 and Dogfather I'd be comfortable lashing to a pack upside-down and not worry about the knives falling out. I removed a bit too much material on the waki sheath so it doesn't have that reassuring heavy click when I insert it. I could tighten it up a bit, but I don't need quite as good retention on that one, so I think I'll leave it be for now.