I ordered the 13.5's from Harold as well. (same length as oem). They are also the same length as the M3 apparently. The important thing I learned when looking at the car on the lift is (at least for the AST's) the mounting point on the strut is orientated 90 degrees from the oem strut. The bracket is not mounted in the center of the strut, but askew, and made to be set running front to back- not side to side. The end links on the XI have a 180 degree orientation, but you really need a 90 degree orientation for the correct fitment with the AST's. The adjustable endlinks from Harold solve this issue.
The length of the link is of less concern with the AST's as the mount on the strut is adjustable. I noticed this issue because I found my RF endlink was coming into contact with my drive axel, actually causing wear on the endlink. It is due to the endlink having to be twisted a bit to fit the mounting point.
Just wanted to pass on what I learned.
XI | COBB | AST | Vorshlag | PFC | STETT | StopTech | Apex | DCI