I put the Citabria spring on today. Simple swap, all I had to do is machine 1/8" off the spacer blocks on the rear bolts. The springs are identical except for the width. New, the Citabria spring is bent 45° unloaded. That's about where the existing spring was at the moment, but of course the narrower Champ spring deflects more under load.
Then I went flying, it's a lot better. I can still make it shimmy if I pull the stick all the way back right after touching down on pavement, so "don't do that", but in a normal landing it's fine. Hopefully it'll hold up better.
It does seem like the way to go, at least for the CB-1. It's American Champion part number U3-1543-S. Note that early Citabrias used the narrower Champ spring, that's a different P/N.