The spring is usually retained when converting these. It will pretty much go back to within 1mm or so of where it did with the original setup.
The carrier needs to be the short version, though, and the bearing needs to be the small diameter one, not the standard one.
If you want straight advice on the topic, ring NPC clutches when they come back in January. He does the conversions so can tell you all the ins and outs. There number is 07 3277 9403