Finished the spacer/reducer today.
It should have now just been a case of machining up a couple of spacers however it soon became apparent that things weren't going to be that easy, things just didn't look right.
Measurement confirmed this, I figured out where the disc needed to go and used washers to fix this distance. This left the rim way off centre.
I need to spend some time working out how far towards the disc I need to go. Using two different methods to measure it it's either 6mm or 9mm out so I obviously need to check my working.
It would be a lot easier to just stick the cast wheels on...