Replacing Radiator, should I replace it THEN do an engine radiator flush

I cleaned out rusted cooling systems with casacade containing phosphorus it can still be found in mom and pop shops, just mix it with water run your car for a couple of days with out your thermostat flush it and repeat also undo the top hose and blast water from a how thru the engine while running repeat until its decent. Also wal mart sells evaporust for 20.00 dollar that stuff works very good and is made for heavy rusted systems, Preston never got the job done like the cascade or evaporust.