Do you have any access to one of the Carafa Specials (I, II, or III)? Since they're dehusked, they give a lot of the dark color and a more mild roast flavor, compared to the high roastiness you'll get from regular Carafa and Chocolate malt. Otherwise, you may end up with more of a really hoppy porter, compared to a Black IPA.
The NG in Halifax (of course) carries the Carafa Special III, I think...