You are correct about the garbage getting into the new radiator. You DO NOT want that. So flush it with a hose till runs clean as advised above, without radiator. Shoot water into the inlet for awhile, then shoot water into the outlet (backflush) for awhile. You can mix and match any radiator hose that helps you get the garden hose gun into it. Use a rag as a seal to keep leakage to a minimum. I don't know anything about a 216, but I second what Ashton says, if it has petcocks on the block, take them out while flushing. You can't get gunk to run thru a little opening in a petcock. Then run engine with bottom radiator hose hooked up to radiator, but not top hose. Arrange top hose (attached to engine outlet) so that it runs into a catchment to watch water color. Take out thermostat and watch the heat gauge. It must get up to operating temp. Keep filling radiator with a hose. Hopefully top hose will start flowing more gunk out into a bucket. Block radiator air flow with newspaper or remove fan. I do not know if this works. Either I just thought of it or I have done it. It's kind of similar to how you use one of those flushing kits. If you could keep filling radiator with hot water, that would be even better.
