I think I answered my own question by looking at both mount designs on Ebay. Apparently on my old mount the U channel was originally bonded to the top piece of rubber, and, the sleeves were moulded into the rubber beneath it. It appears that the new design doen't use them then because the '47 service bulletins say to simply replace my assembly with the new design, and, the parts I questioned would have been part of the old assembly - if it hadn't rotted apart.
Regards:
Oldengineer
Last edited by Oldengineer; 05/14/12 12:28 AM.