Just search for food combining and you'll find no end about it. Shelton's work is available at the soilandhealth site (among others) and most Natural Hygiene books will discuss the subject. Another great resource is TC Fry's Life Science course. Lessons 20 - 43 cover the subject in great detail although you might want to immediately focus on Lesson 23, Application Of Food Combining Principles and catch up with underlying science later.
A quick tip: Anything that you coat with oil will not be digested until the system has processed the oil which might not happen before the food is pushed into the intestines. Before digestion can begin, the vegetable matter will probably start to rot - get broken down by bacteria, the byproducts of which will add to the toxicity of your system.
Pinto beans and potatoes are a bad combination. If you simply must eat them, even without frying the lot in oil, save it until your digestion is fully up to speed.