This extract beer could be converted to all-grain by replacing the dark LME with malt: two-row, 85, 2, 80. The percentages of the black and the chocolate malts also might need to be doubled to take the place of the specialty grains present in the dark malt extract.
This is Kevin Pierson's favorite American Porter recipe. It results in a nice robust beer with minimal effort. Use an American ale yeast such as Fermentis US-05.