i have used slide-a-links before and i like them, they work good at the strip and you can back them off at the street to let the spring do its work.
I dont understand how the caltracs can let the spring work as the bars cant get any longer or shorter as the leaf spring does?

And i dont hink you need calvert springs to make it work, they are just single leafs witch help unsprung weight.
Aldough i believe you need a "weak" spring with alot of wrap up to make it work good.
I dont think a super stock spring is any good for example.