I won a Lancer EVO III Rally Car. You can buy turbos stage 2 and 3 for it, but when you select stage 2 or 3 you CANNOT revert to stage 1. (turbo normal is not there at all)
Dunno if it was like that in the original game also.
The various Rally Cars on the Arcade disc were just the normal cars with upgrades pre-equipped. GT Mode doesn't really support that, so I did the best I could when duplicating them into separate cars - the upgrades are equipped but not purchased or purchasable. They have the extra upgrades from the original car as a purchasable option simply because they're hopelessly worse than the original car otherwise, but the current setup is the least buggy that I could get them. The Arcade Rally Cars were generally a real pain throughout to implement, just to get what are actually badly tuned duplicate cars... but they were one of the biggest requests so I did it anyway.
And yes, the cars on the Arcade disc come with weight reduction stage 2 under the RM, the 306 RM in one of the license tests is the same way. These cars were assembled in the data part by part rather than having to play by the game's rules.