https://www.fillingstation.com/articles/steeringmastjacketbushing.htm

You don't really have to worry about the part of the mast jacket that receives the bushing. I don't think that is the path for the ground.
As far as how deep, if nothing left to measure before removing old bushing, maybe there will be "shadow marks" of where it was. Of course you can figure it out once you see what the plunger/contact and cap and cups need to make contact. The idea is for the spring loaded plunger/contact to be pushed down by a disc or cup to make the plunger/contact touch the metal copper ring on top of the mask jacket bushing and at the some time the disc/cup touches the inside of steering wheel hub. This completes the ground into the shaft threads/spline..... to the body/chassis. The plunger/contact can touch anywhere on the top of the bushing depending on where the steering wheel rotation position.

https://www.chevsofthe40s.com/detail/9347/Bushing_Under_Steering_Wheel_With_Horn_Wire.html

http://chevy.oldcarmanualproject.com/shop/1938/38csm211.html

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