If you look in the MMD Archives, you can find my posting about the
tuning of xylophone bars and the link to an Excel spreadsheet that will
give starting dimensions for bars of a given pitch.  The posting may be
dated, but the physics is not.

http://www.mmdigest.com/archives/Digests/199803/1998.03.21.21.html 
Calculations for Xylophone Bars
1998.03.21.21

Jack Breen
Southborough, Massachusetts