Unless the original starter has some critical fault, rebuild it per the shop manual. Get new brushes, clean the commutator, and reassemble. The aftermarket starters are not good (low torque, rust out, fail early, inferior metal can cause gear pieces and metal bits to snap off, etc)
And you want an 8 tooth starter on a 787 (96 GTX's engine) because it has more torque. 9 tooth isn't a great idea.
If the original OEM starter has completely failed, westside powersports sells used OEM ones you can use instead.