I am not sure what you mean by dial calipers: do you mean dial gauges (clock type face, plunger movement) or Digital scales that mount to the table?
I use 50mm movement dial gauges on my BCA and they are mounted on the end of a square bar at an appropriate locations to be able to measure the table movement in the three axis to 0.01mm. On my other two mills I have fitted three axis DROs using their covers, and I can honestly say that all six mountings had to be designed individually to ensure that they did not restrict the bed movement. But that the protective covers made the mounting/setup job much easier Thm:!
It took me about one hour to make the three mounts for the BCA gauges and about 2 days per mill for the DROs, even with the mounting kit that was provided with the scales. Both have the same level of accuracy, the difference is that my BCA setup cost about 1/10th ;D of one three axis DRO setups' cost but then the console 8) for the digital scales can do things that would take me a long time with a calculator to do on the BCA.
Jo