If you have tooling hole coordinates available use those for your initial pickup and then verify your datums are good to your tooling holes. You can use an Iterative alignment to lock in your datums after picking up your tooling holes.
personally, I use the part datums on the fixture for the iterative alignment because they are what locate the part, NOT the bushings or tooling balls in the fixture base, those are for locating the fixture, not the part.
If you use the bushings/tooling balls in the base to align the fixture, you must check the part locators.
EVERYTHING has a tolerance, even fixtures, automotive fixtures generally have a tolerance of +/-0.002". If the locators are within that tolerance when you are aligned to the bushings/tooling balls, you are good to go. If not, then you really should align to the part locators. While the three A nets are in line, they are NOT single points. Measure 4 hits minimum on each, 3, 6, 9, 12 o'clock, and use those for the level of the iterative alignment.
