Screw a quick connect air line fitting into the block (it's the right thread) and hook up your air compressor to the fitting. Be sure to take the radiator cap off before you turn the air pressure on. You'll clear the clog, and back flush the radiator at the same time.
Jerry

"It is better to be silent and be thought a fool than to speak and eliminate all doubt!" - Abraham Lincoln
Cringe and wail in fear, Eloi- - - - -we Morlocks are on the hunt!
There is nothing noble in being superior to your fellow man; true nobility is being superior to your former self. - Ernest Hemingway
Love your enemies and drive 'em nuts!