What is the actual quantity of granola bar crumbs? Could you substitute regular granola? with added butter or oil?

I believe the recipe is using the smaller boxes which have a total of 12 bars in a box. That equates to just a hair under 9 ounces of granola. Figuring an ounce of granola usually measures about 1/4 cup, you would need around 2 1/4 cups of granola to substitute for the bars. I don't see any reason why you couldn't use whatever plain granola you wanted to make this, since it's going to be pulsed into smaller crumbs anyway. Once you have that, you would continue with the recipe as written.