Brown malt substitute

Brown malt substitute
I was at my lhbs an I was intending to buy ingredients of brown porter homebrew. They didn't have a brown malt (0.5kg) so they gave me amber/caraamber(0.150kg) and carabohemian(0.350kg, I think it was this kind of malt...can it be?)
So what do you say of this substitute? Is it ok? Should be go ok?
This is the full recipe
4kg 2 row
0.350 chocolate
0.350 bohemian (?)
0.250 wheat (they didn't have flaked wheat)
0.250 caramel
0.150 amber/caraamber (?)
30 gr H.N Brewer
30 gr E.K. Goldings
S-4 yeast



And how much corn sugar I need for a 20-22 liter batch?

Brown malt is distinctive, and often imparts a noticeable coffee flavor.  The amber is more like bisquit malt.  Not sure about the other one.  It's still a good porter recipe.

I'd recommend you use the Carbonation tool to calculate the corn sugar by weight. 

Briess makes a seasonal Carabrown Malt which I have seen pallets of in a recent brewery visit.