You will likely have to measure them yourself as the sizes varied from boat to boat.  The stuffing box in Starwhite has two different size nuts.  I was able to order stuffing box wrenches on EBay. 

I was aboard "Starwhite" our W28 yesterday afternoon and checked our stuffing box and the wrenches.  Sorry, I gave you wrong information previously. 

I was thinking of the nuts on "Albatross" our other boat which are different sizes.

The nuts on our W28's stuffing box are both 1 7/8" just like yours.  The pair of wrenches I bought on EBay are 1 7/8" & 2".  As I recall I was unable to find a pair of 1 7/8" wrenches so I ordered the mixed size pair knowing I could shim the larger one.

I shimmed the 2" one down with a piece of scrap aluminum to get a tighter fit, although it worked ok without the shim.  It's been several years since I have needed to use them. When I repacked the stuffing box I used the Teflon packing material, it has worked well and has not needed adjustment yet... (200 hours of engine time).

I made a mounting board for the wrenches (Blue) in the engine room.  Sorry, for the bad photo they're hidden behind some hoses.  

Kevin