Those holes are called stam holes and they are called that for a reason.
The way coolant NORMALLY flows through the "primary loop" is from the
water pump, into the block through the block to the back of the engine then up into the head, now to the front of the engine to the thermostat housing, ou t through the heater hose to the heater core and back to the water pump.
In this "loop" the colant flows around and around...
It only flows out to the radiator in the "Secondary Loop" when the coolant gets
hot enough to open the thermostat..
If you enlarge those holes Except for the ones all the way in the back of the head
it interrupts the normal flow path and that can cause MAJOR problems
read up on the people who have installed Taurus 3.0 engines in rangers without swapping out the Front wheel drive head gaskets.. the FWD coolant path is very different from the RWD flow path/