Agree and disagree about the crater. An ice sheet would have quickly obscured the surface expression of the crater due to erosion and sedimentation. I do believe that the shatter cones and other bedrock effects of the impact would still be present, several of which are quite distinct. To my knowledge none of these have been found.
In Firestone’s book, there is evidence that Lake Michigan was formed by two or three boloid strikes. Also, what about the directionality of the Carolina Bays?