You'll only get Shiny Stones either on Route 14 (Kanto) or for 3000 points in the Pokeathlon Dome. While it's feasible, it will take you a ton of work to get those 3000 points.
As for Rattata, beware of his sucker punch and hypnosis. Even with Raticate, Gengar is still faster than Raticate by a lot, so make sure you EV train him to make up for the 13 base Speed difference.
A lot of people lose their first pokes in nuzlocke runs on SS/HG on that Gengar, so make sure you're prepared 
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