The Bilsteins sold by Firm Feel and others I think are originally for a different application and are modified to fit an A-body by ACD. I say this because I bought a set for my car and after looking closely at them that's the conclusion I came to.
I don't have a problem with that, what I think was done looks like quality work and they are in general a quality product.
I haven't had a chance to drive my car very much yet, that will have to wait until spring. I was going to use KYBs but discovered that they have a lot of gas pressure, turned to be twice as much as the Bilsteins and I think that would have contributed to potentially harsh ride quality.