I could have made a spacer that matched the diameter of the inner wheel bearing race (30mm), but in aluminium, this may have been too "crushable".
I decided the spacer should match the machined face on the inside of the fork leg (33mm).
Rather than a plain tube type bush which would leave the seal exposed to the elements, I opted for a wasted bush that fitted inside the bearing housing (50mm) and reduced to 33mm.
Here it is (needs a cleanup and a buff before I fit it)
This took a long time to make as I cannot hold 50mm bar in a 3 jaw chuck and had to use a 4 jaw which means a long time trying to get the workpiece to run true.