Andrew Jenson provides account of David Whitmer showing him the BOM manuscript and identifying the handwriting of the various scribes.
Andrew Jenson, ed., “The Three Witnesses,” Historical Record 6 (May 1887): 210
David Whitmer brought out the manuscripts of the Book of Mormon. We examined them closely and those who knew the handwriting pronounced the whole of them, excepting comparatively a few pages, to be in the handwriting of Oliver Cowdery. It was thought that these few pages were in the handwriting of Emma Smith and John and Christian Whitmer.