I have a restored 1930 Cletrac 55-40 with original Issacson blade that will be sold at the Antique Caterpillar Machinery Museum (located at Antique Powerland in Brooks Oregon) annual auction on July 27, 2012.  There are over 70 lots of rare Caterpillar and Holt tractors in addition to this rare model Cletrac in this auction.  I am only the third owner of this 55-40 with the original owner being the U.S. Forest Service who used it as a trailbuilder in the 1930's with the WPA.  It is restored back to Forest Service colors and markings.
For more information on this auction and to register for internet bidding go to <!-- m --><a class="postlink" href="http://www.antiquecaterpillarmuseum.org/">http://www.antiquecaterpillarmuseum.org/</a><!-- m -->