Drilled the 4 holes to hold the pitot assembly to the pitot mast. All the parts are steel, so a cobalt bit as slow speed did the trick.
Updrilled the pitot assembly and tapped it for 4 screws.
Then up-sized the holes in the mast, and countersunk the material so the screws fit fairly flush. The mast has curved surfaces, so the countersink isn't perfect.