No matter what topic you pick, your going to have to collect a lot of data so that you ensure that other factors do not influence your results. Just as an example, In college, I wrote a paper comparing net worth to life expectancy. I couldn't just compare how much someone was worth to how long they lived, I had to factor in race, gender, location, job category/type, etc to make sure other factors didn't effect my data or to at least minimize their influence. The question you should be asking is, holding all other variables constant, what effect does height have on wrestling success at the ncaa finals in the lowest three weight classes.
All that said, if you can't find height, you are not going to be able to do this study. I don't want to be a Debbie downer here, but it is.going to be a lot of work to get this type of data because you are going to have to compile it yourself from several places. It may be easier to do something where census data is.easily available.