Yipee!
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All my parts arrived Monday - Sears was very prompt in sending me everything I ordered! Here's the old & new auger gearcase halves:
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Note that the new case part has 7 bolts to secure the case halves as opposed to the old part's 4 bolts. The new case also offers reinforcing bosses to help strengthen the piece's integrity. I messed up the old case half so badly that I just tossed it... 
JDavidson - THANK YOU AGAIN for mentioning this to me & for offering your findings & assistance! 
Snowshoveller - You're not kidding about antiseize getting EVERYWHERE! Even when you think you have it all wiped off, it magically resurfaces...
Marty