If by "normal greaser style", you mean the one Peanut, Ricky, and Lucky use, then it's easy:
Use the ide you have for Lefty, but change /Global/G_Melee_A to /Global/G_Striker_A
It should work just fine.
It won't mess up Lefty's face.
What controls the size and shape of a ped is the character model (i.e. GRH1_Lefty..GRH1_Lefty_W). Nothing else.
Now in the cases where you have to swap stats to change a style, just copy from "Medium/Large/etc." to keep the character's height and everything.