The general desire is to pour concrete on 'undisturbed soil', which typically means non-excavated soil. I would think soil/stone that has been trodden on for 120 years would qualify as that. I don't see why you can't go with pouring on the current floor, taking note of the added comments below.

Basement floors typically don't have metal reinforcing in them. At post or lally column pads the pour would be thicker and may require reinforcement. Evan a one inch layer of pea gravel would establish a drainage plane if things do get wet underneath, so I would recommend that and installing a drainage field with perforated pipe and sump pit (better safe than sorry). And by all means place a 6 mil visqueen vapor barrier over the floor before the concrete is poured; even though the floor appears dry to you now, most every basement foundation/floor is constantly releasing moisture into the home via water vapor. Also plan on sawing control joints to allow for controlled cracking.

How much headroom do you have? Now would be a good time to improve the situation if it is lacking, as you will be losing 3-4 inches if you go with option 1.

Without knowing what the soil in the basement is composed of, any recommendations are being made blind. In general, the best practice in a new home is at least 3 inches crushed gravel followed by 5" of concrete, with 6x6 6/6 wire grid reinforcement. Vapour barriers are commonly recommended but my own engineer advises against them as he cites research showing that they weaken the slab.

Excavation in your case may be a very bad idea; the footings may be close to the surface and you will only undermine them by excavating. (I once bought a home where, unbeknownst to me, the previous owner had done exactly that.) Providing for drainage can't hurt.

Your best investment would be to get the advice of a local professional engineer on how best to procede.