The grade beam is probably the same width as the footer so they can use the same shovel. Given the behavior of the foundation on expansive soil, there may be two working cracks that run along the grade beam. So you will need to thicken the slab next to the grade beam near the lift bases, and reinforce properly. Remember that lift bases carry moments both in the plane of the lift frames from the cantilevered lift arms, and transversely to that from unbalanced loads. So a 24" wide thickened slab at the lift bases is very narrow.
Some comments on monolithic slab/footing design in expansive clay in hot climates:
1. The center of the slab tends to rise over time as the clay comes to equilibrium with the moist soil below. The grade beam will resist this deflection, putting demand on the attached slab. Reinforce the slab and do not saw cut it (fog until final set, then moist cure covered). Use good concrete mix design with moderate water/cement ratio (0.45), water reducing admixture for slump, and proper pozzolan percentage.
2. The perimeter footing will rise and fall with seasonal changes in the clay's moisture content under the footing (less so with deeper footings). So sometimes the slab and building are bearing on the perimeter footing, and sometimes the footing and building load are hanging on the slab and grade beam. So the slab needs to be designed to take the load from the footing. This is one of several reasons that I am not a fan of the massive perimeter footing, since it can weigh more that the building attached to it. I use other solutions.
3. Even with the monolithic perimeter footing, grade beams, and slab, the foundation can still twist in torsion due to differential settlement/soil expansion and contraction. So site grading and drainage is very important. A water barrier membrane can also be used outside the foundation to help keep the soil moisture content more uniform under the foundation. This, combined with a post-tensioned prestressed slab, can give a low material cost solution.
Hope this answers some of your many questions and concerns stated above. Can you use a custom engineered design, or do you have to follow the prescriptive building code?