This may have been covered already, but I've been out of autocross since 2010 because we lost our really good local venue. That venue is back, so I might be prepping my car for GS.
2013 Focus ST has Konis and Bilsteins available. I own a 2014. The difference is Ford changed the front springs and spring perch for 2014+ and neither Koni nor Bilstein seem eager to make a new model.
Can I change out my current suspension with that of a 2013 model and be class legal?