Mill or Lathe?

I’m not a fan of marking out so would locate the three holes on the face that will mate to the tapped part by finding edges and then use the millshandwheels or DRO to position. Start with a spot drill (ctr drill if you want). Then a stub drill which is nice and stiff to get teh hole started true. Then jobber length and probably have to finish with a long series drill. just drill from that one end.

Somewhere around 2000rpm, paraffin or WD40, peck drill and clear the swarf often. Should not need to say sharp well ground drills.

I also don’t much care for spotting through hole positions so again would us eedge finders and then set the position of the tapped holes with the mill.

In short, prevent the drill from bending, start at the exact center of the hole drill from both sides if possible.

That results in:

To much tool pressure will bend the drill so very modest tool pressure.
Good chip evacuation is an absolute must. So peck drilling is needed.
Start using a center drill.
After that use a smaller size drill (3 mm) the shortest you can get.
Drill the hole to just over half the depth, each time using a longer drill.
Bring the hole to diameter using the same procedure
Finish the hole using a reamer preferably from one side only.

An end mill is often more rigid than a drill. Start drilling using a drill and bring the hole to diameter using an end mill is also possible. 4 Flute end mills have a larger core diameter than 2 flute end mills and are more rigid. So the 4 flute end mill is better.

Whatever you do, it is quit a challenge.