I know counter-intuitive... but these are Porsches, they like to mark territory by leaking fluids
anyway...
I found a pic of our alignment system.. it sits flush with the floor...drive the car on, perform alignment back the car off.
When we had this equipment installed, I watched the contractor saw cut, remove concrete slab, remove fill yada , prepare the sub-grade yada yada... place the concrete.. yada yda yada...
The center line elevations of each slab prohibited doweling into the existing slab, which is the situation I think the OP will find himself in
I have some work in progress photos of the pit but cant remember where they are