The protectors extend around the front heat exchanger and can be removed for the required clearance.
@Jeckyll: Buy an m10 if you like, but it'll slow you down, trench, and won't hold the sled up against any decent bumps.
Regarding difference between 136 set back vs 144, the 144 will give better transfer since the pivot point will be further ahead. The set back 136 will also load up your front suspension a bit more - this can be an advantage though, since you will have greater ski pressure for cornering.
As far as people running m10-144, won't be many because that skid just doesn't make any sense.