Hello! I specialize in Tumblr themes. I've also used Quite Big before, and I'm a real fan of it. I've also made modifications to it, so my familiarity with the theme ought to make adding a custom header and footer a snap. If you like, you can check out my portfolio on my page for samples of my work with the Tumblr platform.
I'm on the road so I've set my completion time estimate to be around four days, but I wouldn't be surprised if I can get it done quicker.
Let me know if you're interested!
Thanks,
Way