How do you unhook the steering arm?

to steer the car in right path

You will have alot of play in the steering wheel.

no

Some you do and some you don't. If you can put the pitman arm puller on and remove the pitman arm then leave the gear box alone. If the puller won't fit on it Then remove the gear box.

yes it will if the outer diameter, splines, and taper is the same, you should be ok