If I recall correctly there were no Mach I's built with louvers and spoilers. Some of the judging organizations have let them get by at shows, then later they let them slide if it was a later built car (after the Boss 302 was introduced) then later deducted for any on non- 69 Boss 302's but that is not the focus here. Don't recall anyone ever producing any original documentation of a car receiving with of them on original forms before the original sale of the car.
Yes you see allot of cars that have had them added - a very popular modification