Keep in mind that just about everything here is presented in the form of general guide lines. There are many variables that can affect the process. The 321 method is intended for spare ribs, the more that you trim off, the less food you have to cook and accordingly, the less time. Watch your temps and how the meat actually looks (Meat pulling away from the ends of the bone, burning on the edges or hot spots and so on)
Foil is a great aid. It can help keep moisture in, prevent burning and ease clean up among other things. But completley sealed around food it will also keep out the smoke and its flavor imparting majic.
Let us know what you try and how it turns out! And pics are maybe as close as we will ever come to eating your creations so feel free to post a few.