I LOVE brown porter!!!!! That is a great style.
As far as I know, there are only about two kinds of chocolate malt- the chocolate malt and "pale" chocolate. So I assume the chocolate malt is just that. There aren't multiple malts with that designation.
Anyway, I like your recipe for the most part. I'm not sure about an ounce of challenger late in the boil- I'd much rather see fuggles or EKG, and 1/2 ounce.
I'd drop the mash temp to 152/153, unless you really have problems with overattenuation.