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It has an extended tail, not the Proflex cone. If your shock doesn't have the extension you will have to send it to Stratos.
What I can't figure out is that some pictures that I've seen on this forum in the past show a Helix Expert mounted upside down on a Disco frame. (i.e. with the silver preload adjuster at the top and the air valve at the bottom). I'm not sure how that worked, but I've seen the pictures. Probably wouldn't work with a Pro.