P/S gear backlash adjustment

[NZSquare]

Hi all,
I got an 82 C10 with power steering, and am wondering if I can adjust the backlash on the gear using the nut and internal hex head stud on the top of the steering box.
I seem to have alot of slop in there, maybe 60 - 70 degrees (with wngine off and steering unlocked before anyone asks).

Any advice would be appreciated, my Chilton manual says it can only be done off the vehicle

thanks