I think that it'll need some cocoa butter added to it. In that case, you're better off going back to the store and buying better chocolate than trying to find cocoa butter. Truffles really have few ingredients; the outcome relies on the quality of the ingredients used.

While truffles are often rolled in unsweetened, bitter powdered cocoa, a coating of unsweetened baking chocolate would dominate the truffle. There are some confectioners who use unsweetened and bittersweet chocolate for their coatings, but they've developed fillings that take into account that lack of sweetness.

You can melt a half square and dab it on a truffle. If you like it, use it. If you don't, use the chocolate to make brownies.

I must chastise you, however; if you've gone through the expense of buying heavy cream and good chocolate, then spent the time it takes to make the truffles, why not spend a bit more time and money on real chocolate instead of almond bark? It would take your chocolates to the next level.

I used to use almond bark for my dipped candies, which everyone told me were good. However, when I finally learned which chocolate to buy, where to get it and how to temper it, my candies went from "Yum." to "O-M-G! These are great! You actually made these?!"

You can use the baking chocolate (assuming it is not unsweetened), but you will have to temper it. I find microwave tempering to be the easiest for small amounts of chocolate. Here is a good resource about tempering. http://www.cookingforengineers.com/article/155/Tempering-Chocolate