Don't specifically know about the "Toro," but the decks I've worked on have all been pretty much the same, and the whole arbors have mostly been throwaways. They are aluminum and attached to the deck with hardened, self-drilling, self-tapping, screws that fuse to the aluminum in the acid environment of wet chopped grass. I rarely get a screw out without it breaking off in the aluminum. They are nearly impossible to drill out, as they are hardened and brittle, and the drill wants to dance off into the softer metal and break. Likewise, the bearings fuse to the aluminum too, making replacement difficult. I've usually had to replace the whole arbor assemblies.
When I put in the new arbors, I drill the mounting bolt holes out, throw away the self-tappers, replacing these with stainless quarter-twenty bolts and lock nuts.