The master cylinder in the C20 Vanette is 13/16's. don't know what that is in metric but must be close when you convert it which I am too lazy to do without a calculator.
The van reservior may be a little fiddly as it is designed to fit in behind the dash but you never know Nissan may have been kind enough to run the same size inlets so your reserviors slip
straight in. Why do you want the same reservior set up.
If you are replacing the whole master cylinder I would have thought it didn't matter to much. Rather the flange and bolt pattern that it bolts to would be more important. I seem to
remember a Zoom I think or maybe one of the four cylinder magazines that had a bright orange 1200 ute with a late model motor and I'm nearly sure they stated that it ran a Nissan Patrol
master with the 1200 booster. Don't know what bore size it is but would be worth a look. They run big brakes that work very well.