Radioman,
The one change I would probably have made would be the thumb itself. I would get rid of the bolt on framework, trimmed the pin bosses on the thumb section, installed it onto the bucket pivot via a longer pin, enabling a longer throw and much better leverage ratio for the cyl. If anything breaks on this version I will rebuild it as stated above. The method I used barely modified the actual backhoe where the above method would require extensive welding and modification of the dipperstick and bucket mount.