If you use a Gano filter in the upper radiator hose, that will allow you to trap any crud from the block from getting into the radiator. A Gano filter has a see-thru plastic area with 2 screens in it that lets you know when a lot of crud is trapped so you can clean the filter. Gano's website is:
http://www.ganofilters.com. I have 2 of the Gano filters and they work great. I sure wouldn't just run the engine without some type for filter to keep the rust, etc from getting into the radiator.
Rusty Nelson