it's not really a stout without some roasted barley, but i think it would be great.
a TRUE dunkelweizen would only have 4-6 ounces of chocolate malt.
i would go with something like this:
3.3 lbs of Wheat Malt Extract
3 lbs of Wheat Malt
2 lbs of Munich Malt
however much chocolate you'd like (i definitely wouldn't go over a pound)
0.75 oz tettnanger hops 60 min (bittering ONLY)
if you're truly going for a stout, i would use 0.75 lb roasted barley and 0.5 lb chocolate malt.
what yeast are you using? i would recommend the WLP380 for dunkelweizen. for stout, something clean, like US-05 or WLP001.