you don't need to remove the steering column, but you do need access under the car.
1) loosen the rag joint between the steering column and the steering box. do this from under the car its easier just turn the steering wheel 180 to get to the other bolt in the rag joint. ( good time to inspect the rag joint and maybe replace it)
2) get under the car and loosen the pitman arm from the center steering rod. you will most likely need a pitman arm puller to pop the joint off the center link.
remember to remove the cotter pin to loosen the nut.
the steering column and the steering linkage will now be free.
3) disconnect the power steering hoses. (you have better access from under the car, reach around the steering box with your wrench)
4) lastly 3 large bolts hold the steering box to the chassis rail. release all 3 and carefully lower the box its pretty heavy may want to loosen the 3 bolts then get a jack under it to support it, remove the 3 bolts and lower the jack.
the box will now be free, mark the position of the pitman arm before you use the puller on it and pop it off the box.
you can now take apart the box and rebuild it.
i would recommend a shop manual i can't remember the torque specs off hand.
i would not touch the gear adjustment unless you feel the box is very loose or you have ruined gears inside the box.
usually you take it apart and replace the seals and just reassemble it.
now you can adjust the gear mesh from the top of the box, there is a threaded rod with a lock nut on it loosen the lock nut with out moving the threaded rod then adjust the rod which sets the mesh and tighten the nut when you happy, just be careful the cover is aluminum and you can damage the box or strip the lid out if you go too much.
my box before and after
new hardware from AMK the bolts have a red coating on them with thick washers through the frame
i have accessed the box previously as described from underneath and reaching around the box if you have a 351 or a big block you will not have any clearance to get to the steering box from the top. unless you removed a ton of stuff including the driver's side exhaust manifold to make enough room.
also depending on your exhaust your may need to remove the pipes or drop them off the header collectors or exhaust manifold to make clearance to drop the box down.
also watch the speedometer cable when your down there if it gets in your way you may need to pop it out the transmission and move it around( keep it clean, wrap the end in a lint free rag)