Stone IPA clone recipe: hops questions

I have a friend who is celiac and I'm thinking of brewing up a test batch of APA or IPA with Clarity Ferm to see whether he'll be able to drink it. I was looking at the Stone clone recipes and thought their IPA might be a good one to try, since I've had it in the past and enjoyed it. The recipe calls for two hop additions at 90 minutes: 6 AAU Magnum and 4.5 AAU Perle. For the sake of keeping costs down, I was wondering if I could skip the Perle and just put 10.5 AAU of Magnum in. My understanding is that bittering hops contribute only slightly to the flavor of the beer, do you think that this substitution would make much of a difference to the final flavor? I don't care if it's a spot-on clone, I'll be happy as long as it's tasty.

On a similar note, there are two hops used for dry-hopping this beer: 1 oz of Centennial and 0.5 oz of Chinook. Since I'm planning on cutting the recipe in half, I'll have a bit of both leftover. Could I put some extra in, say double the dry-hopping additions while keeping the proportions the same, and still get a good result? Or would this be overkill?

 

Followup question: the place where I'm shopping doesn't have Centennial whole hops, which are used for dry-hopping. Would you replace those with pellet hops, or go for a different kind of leaf hop? They only have a few varieties of leaf hop right now: Chinook, Citra, Cluster, Columbus, Fuggle and a few others that I think are totally inappropriate.