As long as the radiator is capable of flowing a decent volume of coolant, use it. You'll also get an idea if there are any noticeable leaks you need to fix- - - -water pump, heater core, etc. Rust responds to various types of acid as a flushing agent(I use muratic)- - - -grease and sludge needs something caustic like lye or Trisodium phosphate to cut it. Follow up with a flush with a box of baking soda and plain water to neutralize any leftover acid. The cleaner the system gets the better, but be aware you'll also expose pinhole leaks as you remove the crud.
Jerry
