They must be using dark LME in that kit, otherwise it's awfully light on the dark roasted grains IMO at just 2% chocolate and 2% black malt. That's one disadvantage of using the dark you don't know whats already in it, but assuming it's briess dark LME that would put the recipe at like 5% black plus some munich and additional crystal.
You could use the mini mash to get some brown malt in there. For example replace 2 lbs of the LME with 2 lbs of 2-row/pale ale malt plus 1 lb brown malt, keeping the other grains. That would give you a 4 lb mini mash and keep the gravity about the same assuming you get around 70% efficiency.
edit: I see AIH also sells briess porter LME. Hopefully it's that actually, which would put the original recipe around 6% chocolate, 2% black, no munich but some victory, and quite a bit less crystal than with the dark LME (which at 13% plus the steeping crystal would be way too much IMO). A much better starting recipe. The subs above would still apply.