Those two-dial-gage things work, provided that they are 1) zeroed correctly, which is with respect to the spindle rotational axis, 2) all machine motions PERPENDICULAR to the table surface are locked, and 3) the table surface is parallel to both the machine along-X and along-Y motions.
From that point, it's a matter of 1) putting a parallel spacer on the machine table so that one of the dial gage plungers is resting in the center of the spacer, but won't extend far enough to contact the table. Lock the knee, lock the quill, and be sure the machine head's nod and tilt adjustments are locked 2) Zero the dial gage contacting the parallel spacer. 3) Rotate the spindle to place the second dial gage plunger in the center of the parallel spacer, and if necessary adjust the dial gage in its holder so that the plunger can contact the surface of the parallel spacer but not the surface of the table. 4) Zero the second dial gage. 5. Rotate the spindle through a full revolution, and verify that both dial gages are zeroed when contacting the parallel spacer.
From this point, I'd recommend removing the parallel spacer, raising the knee until both dial gage plungers are slightly depressed, lock the knee, and then have yourself a ball making head nod and heal tilt adjustments.
The same setup process works if you want to set the head to an angle, except that you'll almost certainly need to lower the knee to sweep your sine bar or sine plate.