Probing that one tiny hole won't be very effective at removing 50+ years' worth of crud that has accumulated all along the bottom of the water jacket. Even if you get coolant flowing freely from that one spot, how do you plan to handle the other areas? The only effective way to clean the water jacket is going to be by pulling the cylinder head and the freeze plugs, and doing a LOT of probing and scraping to dislodge the sediment all along the bottom of the block, not just near the drain plug.
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
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