785's are 9.5" compressed and 14" extended. There is some variation in that up to 3/16". The 09 and up chassis will take the 9.5" collapsed with a stock 16" or 18" rear wheel/tire combination with no problem. On the 08 and down bikes be sure to check fitment/clearance.
They will work with your 12. You will more than likely have to remove the lowering kit unless your running a 180 60 16. With that tire I've been able to use a 1" lowering kit. There may be a 17" equivalent. I've yet been able to use a lowering kit with a 18" and any tire.