Wouldn't you have to replace the drive gear also?  Which would require removing the back housing off the t-case.

Yeah, I thought about that after I ordered the new one from the dealer.  On the way home I was wondering, if the new gear has 32 teeth as opposed to the stock 18, it must be a bigger diameter.  So it would make sense that the drive gear would have to be smaller to mesh with the new speedo gear.