The springs themselves are different lengths (Bully to OC style.) Bully uses .500" length springs, while the OC style clutches use .600." I hope I am correct on that. As Mike said, they are considerably different when held side by side, but to the untrained eye, if you were to only look at one, you may not notice the difference in length.
Also, when measuring wire diameter on a spring, check it in the middle of the spring and consider the thickness of the powder coating (or whatever color method was used.) zinc, chromium, nickel plating, etc will add very little to the wire diameter dimension, while powder coating can add enough to make you think it's the next wire size (ie .086" - .091.")
Thanks Mike, for offering your chart on the gold springs.
Much appreciated!
Hopefully others will follow your lead.