Who raced their bikes stock in the day? If we're about "recreating the era", then prohibiting period-possible mods is against the spirit of the era.
My reading of the rules prohibit Lectrons in Evo, but not in pre-78. The carbs were available in 1977 so there's no argument against them. However, the Evo rules say that "bikes must be OEM" - most people's understanding of that incredibly ambiguous rule means that you're not allowed to perform carby swaps.