I would also flush the ENGINE as well. If that's not been done, it's worth doing. And if the engine is really dirty, go ahead and flush the radiator as well, since it is now contaminated. Get it all as clean as can be.
First thing I did - the entire cooling system resembles Hi-C Ecto Cooler, just the way it should, but I guess you can never flush enough so I may do another run with a reverse flush. That first flush was how I discovered the previous owner blocked off the heater lines at the engine instead of just running a loop.
