Any of the methods shown above will work.
I'm not criticizing , I don't want polemics , just sharing the solution made available by Stellafane site and which I believe is the best.
Simple , elegant and effective - the center bolt as suggested in the ''Build a Dobsonian'' of ''stellafane.org''.
It is very easy to retrofit.
It resembles the solution posted by xrayvizhen -see post #4.
But in the drawing the T nut is in the wrong place.
The T nut should be put on the upper face of the ground board as suggested by Stellafane.
The nut should stay as per drawing.
No need for any bushing into the rocker base.
Actually one need a radial play between the rocker base and the bolt which should be large enough to allow the rocker to sit only on teflon pads - that is the bearing.
Not the bushing.
The bushing and the teflon pads are working one against the other , with bushing and teflon pads you have double determination.
This is not working well in real world.
At a moment the bearing consist of teflon , few degrees further it consist by bushing.
The Stellafane center bolt could be retrofitted.
I done it already to my 125mm Dobsonian telescope
I made many observations with the 125mm Dobsonian after retrofitting this type of center bolt and is working great.
And is under implementation on the 8'' F/6 Dobsonian.