I’d like to know the answer to this also. We’ve recently paid to have our gland “serviced” as it was a requirement of our purchase survey, but we’ll need to tweak it to get the drip rate correct.
For my 321 I bought a cheap big stillson wrench from a discount online tool store. It is 18″ or 24″ long and works well because of the high leverage. Damage to the nuts does not seem to be an issue.
Some time ago Richard Bartlett had some spanners made out of plate steel, we dont have any now but it may be worth investigating getting some made, I also struggle to find suitable wrench’s to undo the stuffing box nuts.