I am definitely the best candidate for this project. Why? Well, it's a very simple reason: I am a Grammar Nazi. I drive everyone absolutely crazy with my insistence on using proper grammar and spelling. Sometimes, this is to my detriment. In this case, however, I truly believe that it makes me the answer to what you're looking for.
Now, there's a question you might ask. "So what if you're a Grammar Nazi? Do you have any real experience editing and proofreading?"
Fortunately, the answer is YES! In high school, I edited my school's online webizine on a semi-regular basis. I then proceeded to write articles for my university's online newspaper, and usually proofread the articles on my own before submitting them to the paper.
Of course, editing newspaper articles is different from editing articles with language similar to the spoken word. That's where my skills as a playwright come in. I co-wrote our school's annual play production and placed an emphasis on very natural dialogue. In 7th grade, I rewrote Shakespeare's 'The Merchant of Venice' in a way that didn't alter the story one bit, but made the language much more natural and understandable.
If this isn't enough to convince you that I'm the right person for the job, well, know this: a job like this is more like a dream come true for me. I love ensuring that a piece of writing is absolutely perfect. I hope this proposal sways your decision in my favor! Please get back to me as soon as you can.