As one argues the merits of the Osprey, the decision must be viewed with regard to the platform its replacing. The -46 is old, restricted (at least it was in peacetime). Many have bullet hole patches from Vietnam.
As far as the chin turret, I believe that's being looked at in a later block. The data should already be there from the USAF I believe.
As Green night mentions, I remember the -53E in its infancy. The aircraft enjoyed a terrible reputation in the eyes of the media yet is now well proven.