Have you talked to the dealer?
I recently changed the idler pulley on my older 440b, and the one I go from the dealer was a significantly improved design, although it did require a modification of the tensioner's idler arm. Bobcat sells this new arm, but it is pricy. I modified my old arm myself to make it work.
My machine uses a B-width Vee belt, not sure if this carries over to the 463 or S70. I recall reading that Bobcat changed over to a serpentine-style belt at some point on later machines, but I am not sure when. That may preclude you going to a full S70 set up if your machine is currently using a V belt.
FWIW - SR