Your malt bill looks pretty good. I'm still tweaking my porter recipe, but my hop bill is 20 IBU's of Nugget at 60 minutes for bittering, 10 IBU's of Willamette at 15 minutes and about 7 IBU's of Cascade at 5 minutes. This is for a 1.045 OG, for something in the 0.75-0.8 BU:GU range. I don't find it anywhere near a Black IPA in bitterness or hoppiness, but it does have a nice level of hop bitterness and late hop character. I target the "Black Bitter" water profile in Brunwater.
I think the key for "americanizing" your porter recipe is to switch to a clean yeast, and maybe adding a moderate charge of West Coast-type hops later on to have just a hint of American hop character. Something like Cascade/Centennial/Amarillo. That's my tastes at least, YMMV.