The AD series crawlers were built from 1937-1959 according to information that I have. It is my guess that the ADH came out in the late 40&#039;s and stayed in production until the mid 50&#039;s. The regular Ad had a 42 inch track center while the ADH had a 50 inch center. The serial number that you gave doesn&#039;t correspond with any of my data. 1954 models begin with serial number 450000 up. The expert on Oliver Clectrac is Landis Zimmerman. He can help identify the year and probably has the parts that you need. He can be reached at 717-738-2573.<!-- s:D --><img src="{SMILIES_PATH}/icon_biggrin.gif" alt=":D" title="Very Happy" /><!-- s:D -->