Just wanted to chime in here and say that I had similar situation.
What I did was tear out the radiator, housing, hoses and so on. Then rigged a hose on the outlet of the pump(replacing later) with tape over it to keep it sealed in.
Then I rigged a funnel for the housing inlet and poured evaporust into the block and let it work its magic for a bit.
Reassemble all new parts (core,hoses,heater lines,heater valve,thermostat, radiator, and so on)
Finally what was suggested to me which I think is brilliant is to install a filter in the hose where the coolant goes back into the radiator. As you will more then likely continue to get goop long after you flush it.