The part number for a Melling 1 1/8" disc type freeze plug is MEP-10. It will fit the counterbore with a little careful grinding on the perimeter, and a firm tap with a hammer will expand it.
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!