Due respects to Bookbinder, but I wouldn't even think of using a 7" core drill unless you really must have a clean hole. You'd need to rent a big ol' drill to drive it.
As often, I'm with bhg on this. A ring of 1" holes using an SDS drill. An SDS is far more powerful than a simple masonry drill.
A longish cold chisel would be fine to complete the hole, but a small demolition hammer (Kango or Hilti or similar) would be a lot easier.
Actually, a 6kg SDS demolition drill would be fine for all of it.