My first postknocking setup was a Wrag (200kg weight) on a Zetor 7045. If I remember the flow was around 20 L/min. The problem was the weight was painfully slow getting to the top of the mast. Wasn't too bad if pulling the weight from the bottom of the mast as momentum seemed to help but if lifting of the top of a strainer post for example it wouldn't do it. Was that a pressure problem rather than flow perhaps as said the ram to lift the weight is pretty short stroke so would have thought there would be enough flow.
In the end Wrag built me one with a PTO pump mounted on the knocker and that was ace
Sounds an interesting project though and would be a handy unit for awkward jobs that big setups couldn't entertain.