I did this on some 140mm 2009ish Revs and it turned into a bit of a strange one…
Despite all the information I could find, including dimensioned drawings of the two forks, the 140mm dual position Sektor coil spring assembly was approx 20mm shorter than the old air u-turn assembly.
I even ended up on the phone to SRAM tech support, who were next to useless in this, as all I wanted to know was the correct dimensions of the two assemblies and they couldn’t, or wouldn’t, give me the info… all they would tell me was that it was impossible to do the change…
Anyway, in the end I used a length of threaded bar and a threaded spacer to get the extra length and just used an external nut to assemble it into the fork. It might not be the most elegant solution, but it works, and has so far survived a number of trips out, including a trip to the Alps.
One thing to note, the DPC spring does not have a negative spring as part of it, and uses a negative spring in the rebound assembly, but that was dead easy to fit, just make sure you have the right number of spacers under the negative spring.