if there are any drain plugs in the bottom of the block, open them up, too. a lot of crap settles in the bottom of the blocks that should really get cleared out when the coolant is changed.
i like to drain al lthe coolant and fill it back up with straight water.
then drain it again.
then take the thermostat out and jam the garden hose in there with all the drain plugs removed and petcocks open and run the hose until the water runs clear.
put the thermostat back in and hook the hose up. take off the heater hose that is the highest up.
then i fill it up with the water/antifreeze mix until it comes out of the unhooked heater hose- this means that the engine is full and there are no air bubbles.
hook the heater hose back up and top off the radiator.
start it up and watch the level- if it starts to drop down, then keep it topped up. as soom as it doesn't go down any more, it is full.
put the cap on, fill the overflow to the "full cold' mark, and let it run until it gets up to temp. a quick drive around the block will warm it up a hell of a lot faster than just letting it idle.
if it holds pressure, you should be good to go. recheck the water level after it cools down and top off as necessary, but it shouldn't be low.