Pin-type spanner wrenches are all over Ebay, both fixed span and adjustable types. The thin open end wrench in the picture is used to adjust preload on the pinion bearing, not the carrier bearings on both sides of the ring gear. I learned to adjust the ring gear backlash by moving the carrier assembly back and forth and checking backlash with a dial indicator, and then tightening both adjusting nuts one notch to preload the bearings. It's worked well for me that way since the mid-1960's.
Jerry

"It is better to be silent and be thought a fool than to speak and eliminate all doubt!" - Abraham Lincoln
Cringe and wail in fear, Eloi- - - - -we Morlocks are on the hunt!
There is nothing noble in being superior to your fellow man; true nobility is being superior to your former self. - Ernest Hemingway
Love your enemies and drive 'em nuts!