Thanks to Barb Schmidt for the only identification of Charles D. Crane we
have. The MTP does not have his letter of inquiry to Clemens. And the
second, follow-up letter we know about comes entirely from a Merwin-Clayton
Sales catalog of 15 December 1911 which reads:

A.L.S., 1 p., 8vo. Hartford, Jan 24. to Rev. C. D. Crane.
 "Dear Sir: Please leave out the 'B. B.' book and all reference to it. This
will save me from having to answer the letters of inquiry.
 "In the place of it I desire to put 'Pepy's Diary'--the condensed edition.
Truly Yours, S. L. Clemens."

We know no more about "B.B." than that.

Cheers,
Bob Hirst