So my steering box received a new caster wheel shaft as the old one had some pitting on the flanks. The old bushes in the housing and in the aluminium cover where a little worn so I popped them out and machined up some new plain bearing.
The aluminium backing plate
setup your job in a lathe, machine a little of the aluminium out to clean out the remains of the dimples from casting and machine the OD of a bush to suit (see photo above). I would recommend the smallest interference fit you can manage as its very thin walled aluminium you'll be pushing it into. I then also used a retaining compound to minimise any chance of turning in the housing. To make the ID concentric to the main housing's bearing, setup the aluminium backing plate using the spigot and face of the flange, then bore out.
The main steering housing
The bearing for the housing is a little simpler. measure the bore, machine the bearing with a interference fit on the OD (i still used a retaining compound) and a tad undersize on the ID maybe .02 ø and then ream out to desired clearance.
make sure that when you box it all up the caster wheel shaft doesn't become tight when the backing plates spigot is pulled up. if it does! you can do it all again! ; )
The end float on the driving spindle should be checked even if it has not been changed. I found mine to be have a end float of .2mm!
It seams like a design flaw that on the 'support housing' the plastic bearing is protected from the mud and water under the haflinger by the 35x25x7 lip seal. any water that finds its way in between the support housing and the steering box housing will run down and collect at the bottom of the houseing (near the steering drop arm) and rust the caster wheel shaft's bearing journal. I will be filling the support housing with marine grade grease and using liquid gasket at the support housing/steering box.