I recently purchased a 816s with manual lift and wanted to know if anyone had any pictures or information of what's required both parts and labor to add hydraulic lift to a manual lift 800 series tractor.
It can be done, there are manuals on old Gravely manuals website and you'll need to source parts probably from eBay if you don't live on the east coast (lots of Gravelys on east coast, not so much on west).
As a start, you will need a cylinder, valve, pump, reservoir, and lines. Then you may need to modify the existing linkage. In short, it takes a fair amount of work.