Autoweek states the exact same bore x stroke as the 1M and the piece in this post. The 80 mm bore above is obviously a typo and should be 84.
http://www.autoweek.com/article/2013...NEWS/130929883
That article also talks about a more than 200 lbs lighter CSL being considered with lightweight seats etc. I think Scott26 has hinted at this as well.