Mild ale malt was/is so nearly identical to pale (just made from a lower grade, higher protein, cheaper barley) that you can simply substitute more pale malt for the mild. The "caramel" in that recipe is not caramel malt, it's brewer's caramel, an insanely dark liquid coloring used in microscopic amounts to adjust the color of the beer before packaging. Ignore it, it's not available to homebrewers. Brown malt will not have a desirable effect here. Not sure what you intend to do for the invert. I've been making it, and honestly would not recommend the effort needed to reach no. 3 color; flavor and fermentability are not significantly different in the darker colors.
Here's how I'd rework Ron's recipe: Pale malt only. Make no. 1 invert, or just use demerara sugar at 75% the weight of the invert syrup called for. Use a small amount of debittered black, or better yet Midnight Wheat, to reach the desired color.
Ron's books and blog are fun, aren't they?