The mod got the nod from Mr Comstock. (I wanted to avoid cutting the tube)
I had some time last night so milled the D/S bush until it could be collapsed easily (and carefully) and all but fell out.
The blind D/S will be a little more tricky.
I wonder why Norton did not use sintered bronze.
The picture is not clear enough but the machining marks were still visible from when the case was bored, to the right of the oil feed hole is raised alloy from when the bush was installed cold and raised the surface as it went in.
The replacement bush will have the engine case heated and the bush will have the outer face of the hole chamfered to avoid that.