After a couple emails today asking about C7 double ballnuts I checked with Chai and he carries them too so I put in an order for a new set, should fit easily with just a little more pocketing of the saddle for the X ballnut.
The standard C7 ballnuts have very low backlash themselves and much less friction but this is another option to try.
The pic should be similar but don't know for sure till they show up.
I won't be doing my Z, too much work for me now.
Hoss