In an AMA sanctioned race reeds would be considered a MOD...But almost all races I've been to are mod class rules even though they are AMA. They are considered MOD unless stated STOCK. For instance, when qualifying for Loretta lynns you will ride both stock and mod...But usually at local races you ride mod.
Its totally different in the 50cc classes because by AMA rules there are no MODs allowed whatsoever.
Of course there is California stock...AKA .080"over. Wink. Out west the rules are a lot more grey but then they are only AMA during LL qualifiers.