It's a real tricky deal to be honest(and not cheap in the end). I spent quite a few hours just doing math on this stuff and still didn't get it right the very first time, but it did point out my miscalculation and made it easier. Only cost me a bent shock shaft that time.
You have to be real careful what you do with the front arm too. If you change front arm lower mount location you are affecting the swing axis of the skid, which could result in some problems. If you do the geometry on this stuff it makes it obvious what needs to be done. It's a very complex system when you start doing that though and you get a different perspective on the achievments of the design engineers. By the time I was done, I had to build a new rear shock(longer) and needed different springs with a longer long arm as well as longer link arms. The linkage ratio was different and became more linear rather then so progressive later in the stroke which required stiffer springs yet. The gain was 2.85" on the swing axis (if I recall correctly) and about 1" in ride height. The truth...it was a lot of work and some of it was frustrating as hell but I guess it was fun. This is the most you can get from it using the stock arms. I'm going to see if I can find any longer arms used on different models to gain even more travel.
2.85" sounds like a lot. It's not really because this is measured on the swing axis. If it was 3" of true vertical travel then it would be BIG it looks BIG though when you say it's gone from 13.5" to 16.35". You can feel this difference but it's really not a BIG gain. But heres the catch....my sled (97 ZR 440) sits about exactly as high as a 02 ZR 800 CCe in the rear, but I have slightly more actual travel due mainly to a linkage ratio change. A M-12 seems like such a good investment sometimes!!!