Concrete – Brick pillars gone now what

Base on your description:

1. Concrete strength does not appear to be an issue. With a minimal 2500 psi concrete the entire safe could bear on one square inch.

2. The size of the footing depends on the bearing capacity of the soil. Suppose the soil has a bearing capacity of 20 pounds per square foot. Then the foundation would need to be 25 square feet. Other soil bearing capacities would require larger or smaller minimum footings.

3. Placing a new foundation near an existing often has substantial engineering implications. The forces overlap on a portion of the soil because the bearing capacity of a soil is a function of it's ability to distribute loads. Consultation with a professional engineer may be in order.

You can always use a masonry grinding wheel and a level, but be warned, there will be a LOT of dust! You'll want to seal off the room from the rest of the house, open the windows, put fans in the windows, wear goggles and a respirator. They sell shrouds that you can hook up a shop vac to the grinder to get a good bit of the dust, but it's still bad. And at that point, it might take you 2 to 4 hours. I leveled some high spots on my basement floor and man, what a time waster! You may be happier if you rented something bigger than a grinder, or used something like below - the bonus being, if you used aggregate, it'll shine through after grinding.

You could also rig up a sled if you would like, where you attach something flat to the back of your grinder and then run it along something flat and level independent of the table surface, like below. Unfortunately, I don't think they make diamond cup bits for routers, but you might be able to use a diamond hole saw with a 1/4" shank if you want to use a router/sled method.