The active ingredient in all the commercial rust treatments is phosphoric acid. The real stuff is available on Ebay. Mix up a pretty strong solution of it and circulate it, then once the engine is clean enough to satisfy you, flush with clean water and neutralize the acid with a box of baking soda mixed with water. Refill with a 50/50 mix of water and antifreeze.
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!