Optimum air speed and other dumb questions

The Class the car is being built around is replicating racing in Australia between 1965 and 1972, cars that have proof the make and model raced in the period are ellidgeable, most items that are free (carbs etc) had to have been available in this era.

The vehicle in question is a 1967 a body 4 door.
Exhaust, I was planning a custom set of open headers in time.