Here we go:
Bang a nice 25mm drill through the middle:
Bore out to 36mm:
Spot drill the hole centres and drill through 3.5mm (for M3 clearance). Set it up carefully using the Renishaw probe:
The 4mm spot drill will only just create the dimples without hitting the edge of the register, so their position is critical.
Deburr - job done. Nice:
Those fixing holes are spot on, despite the jobber length Banggood drill I used.
Right - next....