Can you buy a hyd thumb for say a link belt 800x2, or cat 385, komatsu pc800 etc. I saw one on a cat 5110b, but i believe that was custom.
A local demo company has progressive link thumbs on 3 of there volvo 700's 1 link belt 700 and a hitachi 1200. Im sure u could get one for either 800..
Many companies will build them for that size new. I have seen used ones for sale at Deloss equipment in Barstow Ca. If you are doing big rock, it is handy.