Ponchogl - Your transmission code 590874, as you mentioned above is confirmed as a 1937-39 Commercial Truck 3 speed. I will try and dig in to an early 1929-46 Chevy Master Parts book to see if I can find anything related to this transmission, the odd bracket and leak issue tomorrow.

Hard to say if that is a crack in the case or not as that's where the normal casting mold part line is.

BTW - Your engine serial number beginning "GAA" indicates its from a 1949 Chevy passenger car per the 1949 Chevrolet data PDF.

~ Dan
1951 Chevy 3 window 3100
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"My Grandpa Carl's Truck and How it Became Mine"
1966 Chevelle (Wife's Hot Rod) | 2013 Chevy Silverado (Current daily driver)
US Army MSG Retired (1977-1998) | Com Fac Maint Lead Tech Retired (1998-2021)