'60 Apache 2WD front wheel cylinder bolt size

[Desert dog]

We're moving on to the front brakes and have run into a conundrum. The large bolt holding the wheel cylinder's in place appears to be an odd size. A 1" 6 point socket is loose and a 15/16" six point is too small. Is it possible this is a 31/32"?
My cursory calculations show that a 25 mm falls roughly between the two above mentioned sizes so I'm going to purchase one. It looks like
I'll have to grind the chamfer off of it though as the bolt faces are pretty shallow.
Any input would be greatly appreciated.

Regards,
Desert Dog