Ken,
I'd machine a male square to fit the square hole in the part. If you need two holes at right angles, then hold this fixture in an indexer so you can do the 90 degree index.
Once you set up to mill the square on the fixture, and drill the hole in it, then do not disturb the fixture. Just slide your real parts over it and drill them, too.
It appears as though your part has an axial hole lengthwise through it, so that means you could add a threaded stub to the end of your male square fixture, to retain and clamp the part whilst it is drilled.
First you get good, then you get fast. Then grouchiness sets in.
(Note: The opinions expressed in this post are my own and are not necessarily those of CNCzone and its management)