Looks and feels pretty reasonable considering.
The back plate is diecast. It's little more than a chip guard.
With the plate removed and the 3 drive pinions out of the way, the scroll bevel gear should come out.
Into the 4 jaw on the lathe.
And bore it out to 36mm. Plenty of meat left on the central boss.
Not a perfect finish but it's a clearance hole and can't be seen easily.
Now put it back together again.
And back in the box until I'm ready to mount it on the 4th axis.