Well now I've gone and done it! Put my SS12 back together and mowed today. When I got done, dang if both of the rear hubs hadn't walked inboard almose all the way. I thought I had them tight but when I jacked up the rear they were both able to wobble a bit on their axles. Got into single-minded "got to get these hubs tight" mode and wasn't thinking about the fact they're cast. Everyone else will already know the result. Cinched the left one down, probably more than I should, but it tightened up. Cranked on the right one, still loose, crank some more, still loose, give 'er hell!, and of course, POP!
On the one hand I'm mad at myself for breaking it, on the other hand, if it wouldn't get tight I was going to have to do something to solve that anyway. Are there any other hubs that fit this tractor but aren't so inclined to crack? This is the high/low with keyed axles.