I just finished breaking up my basement floor. It was poured in the 40's on a severe angle aiming towards a center floor drain. I want to repour a new one even so the area is more usable.

After breaking it up I see that the old floor sat perfectly on top of the footings around the perimeter, which means the center floor drain must be equal with the bottom of the footings or even lower!

So my question is can I excavate the necessary amount, then re-pour the new floor so its finish surface is equal height with the top of the footings?

Yes, but what will you do with the joint between the floor and the footing, and is the top of the footing finished the way a floor slab should be finished? Ideally, the floor slab should brace the bottom of the foundation wall, and ideally, there should be four inches of gravel between the bottom of the slab and the top of the footing, and the vapor retarder should be turned up the wall and taped to it. That's about three "ideallys" that you'd be missing.

No the top of the footings is not the nicest finish like it will need to be, but I can go to work on that with my grinder afterwards.

As for the vapor barrier.... there was nothing there before and I never had water issues wicking up through the slab.

And the gravel will still be under the new slab.... 3-4 inches worth, then a 3-4 inch slab right? Should be able to squeeze that all in the depth of the footings I hope.

Four inches of gravel is the accepted standard, as is a four-inch slab, and if you don't install a vapor retarder, you will regret it. Besides, it's a code requirement. Suit yourself, but standards arise for reasons, and it's best to abide by them.

In some areas, it is required to have 3.5" of concrete slab poured over the footing and against the foundation wall. This was a result of the poor structural performance of the foundation walls with a water collector ditch around the perimeter of the basement slab. This 3.5" bearing area is important, because there is really no structural requirement for the there to be a shear connection between the footing and a foundation.

Whether or not it is code in your area, a vapor barrier is an excellent idea and is cheap. If you ever put down flooring it will be necessary.

So what your saying is that because there is likely no structural connection between the foundation walls and the footing they sit on, that slab floor acts as a support to hold the foundation walls in place when it sits on top of the footings and up against the side of the foundation walls?????

As for the vapour barrier, I have no problem putting that down there, it will just get tricky trying to seal it nicely against the sides of the footings where the slab floor will terminate, rather than sitting on top.

your floor should be on top of the footing no even with it. This prevents the bottom of the wall from pushing into the basement should the pressures from wet soil and backfilling cause the link of the block wall where it connects to the foundation to fail.