The tire specified is a 23x8.50x12 . If you can find an HONEST sized tire, that would probably do the trick. I briefly tried a 24x12x12 tire on my Massey 12, but the sidewalls rubbed on the seat pan. I have a 25x10x12 ATV tire on currently, and I'm not sure the deck would fit. I'd say that if you are set on installing the tires and the deck at the same time, you need to stick to stock tires.
If you're using the factory offset wheels for the 12 the biggest you can go is 23-10.5" wide,but not the tru 10.5 tires.Depending on which tires you get they have different widths.They are supposed to be 10.5,but are actually only 9.5" wide.The ags I have on my 10 are marked 10.5 but measure 9.5 and fit good. .Check with the tire manufacturer on the actual width.