WOW! What are you mowing? That assembly uses 4 bolts to hold it onto the deck shell. Did you pull the complete assembly up under it and chew it up? I think that is one of the better decks with the large rollers on the back. This is mine that I replaced all the crappy OEM rollers with new rollers with sealed bearings. The shaft that the rollers go on is just a piece of 3/4 rod IIRC and can be replaced for about $30.
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The later 3K machines did away with the rollers and went back to the anti-scalp wheels but those machines have a deck height adjustment stop on the floor of the tractor. I'm not sure if yours has that. I know that when you back up with the deck lowered the rollers can sometimes catch on things but I wouldn't think it would pull it off. Do you have any pictures of what it looks like now? There is a guy selling the newer type deck that is NOS in Tennessee on Ebay now but I don't know if that will fit your machine.