Ok. So this is a case where IMO you should follow the schematic. You could tweak values to account for parts costs / availability. Manufacturers do that all the time. But if you're re-creating an existing circuit you should copy the circuit as closely as is reasonably possible. I'm not sure if I would use 250 Mohm in this particular case. I think I might actually parallel 400 || 500.220 M.ohm is used in the U47 FET for example.
At the moment I am waiting for a reply from my contact in Taiwan.
As soon as I know more, I will let you know!