As far as kits it just depends on what you want exactly 2.5" should be fine with a stock set up. The link I'm attaching is a link to summitracing.com and it's all the exhaust systems they have for our trucks. Now typically I've learned the larger the muffler the quiter it will be, it doesn't show on here but you could even search magnaflow and flowmasters main websites and might find some kits there.
http://www.summitracing.com/search/d...1977/model/c10