I'm wondering if something could be done about forcing some race restrictions.
The game doesn't support any restrictions other than what it currently uses - aspiration, RM / non-RM, power limit, drivetrain, and entry whitelists.
The manufacturer race entry whitelists are limited to a maximum of 32 cars, while Suzuki alone has 20 Kei cars (as RM versions are counted as separate entries in the list). The Impreza one-make event likely doesn't have a RM version for that reason - there are way too many Imprezas to fit in one entry list if RMs are included.