Which item will best for a Charziard who was migrated from Firered to Pokemon Diamond?

I am trying to look for the best item for my Lv. 51 Charziard who was migrated from Firered, To Pokemon Diamond. Oh and another Question if you migrated a pokemon from a GBA game does the Pokemon gain more ex. points, if it is, does anyone know how much more it gains.Which item will best for a Charziard who was migrated from Firered to Pokemon Diamond?Give him Charcoal, i guess. And yes, your pokemon does get extra experience points if they were migrated. I do not know how much more.