Even if we had the same number of tornadoes and tornado strengths, and even given the population growth and sprawl that has happened since 1974, I do not think we would see the same number of fatalities, and probably not the same number of serious injuries.
The warning and detection is light years ahead of what it was then, and medical advances, better emergency first response, emergency treatment, etc. would limit the number of fatalities-some of the people who died then would have survived with faster and better treatment available today.
Also with the mass media we have today and instant communications with various devices(cell phones, computers, etc) more people would be aware of what is going on, and be able to take some kind of measures to protect themselves and get to some kind of shelter.
*The only exception to this I believe would be a worst case scenario thing, with a strong tornado striking a sporting or entertainment venue with thousands of people who are simply unable to get to appropriate shelter in time, and with a catastrophic structural failure like in a large arena, auditorium, concert hall, etc.
The damage totals could very easily be greater given urban/suburban sprawl, overall population growth, and simply more developed land to be hit