AI'd like to make the Margarita cake in the WASC doc for a birthday party but I see it calls for frozen margarita concentrate. Unfortunately I can't get that in my area. I'm thinking about using the regular liquid mix but I'm not sure if it's concentrated enough. Thoughts? Should I make a reduction of the liquid mix first? I'd hate to throw off the whole flavor.

I haven't looked at the recipe you're referring to, and don't have an answer to your question, although with all the expertise here, I'm sure someone else will.  

However, this is a Margarita Cake I've made, and it was quite good.  It doesn't use the mix, but has other ingredients to give it the flavour.

I found it online somewhere.  Wish I could credit it, but can't remember where, unfortunately.

Margarita Cake

Ingredients:

• 1 package (18.25 ounces) plain yellow or lemon cake mix
• Half a package (3.4 ounces) vanilla instant pudding mix (4 tablespoons)
• 1/3 cup granulated sugar
• 2/3 cup water
• ½ cup vegetable oil
• 1/3 cup fresh lime or Key lime juice
• ¼ cup tequila
• 2 tablespoons triple sec
• 1 teaspoon grated lime zest
• 4 large eggs

Place a rack in the center of the oven and preheat the oven to 350 degrees F.

Place the cake mix, pudding mix, sugar, water, oil, 1/3 cup lime juice, ¼ cup tequila, 2 tablespoons triple sec, and the lime zest and eggs in a large mixing bowl. Beat with an electric mixer on low speed until the ingredients are combined, 30 seconds. Stop the machine and scrape down the side of the bowl with a rubber spatula. Increase the mixer speed to medium and beat for 1½ minutes longer, scraping down the side of the bowl again if needed. The batter should look smooth and thick. Pour the batter into prepared pan(s), smoothing the top with the rubber spatula, and place the pan(s) in the oven.

Bake the cake until the top springs back when lightly pressed with a finger, 42 to 47 minutes. 

AHmm that sounds like a good option thank you!! There's no pudding mix here either but I do have a good homemade dry version to fix that :)