active dry yeast vs instant yeast
Active dry yeast and instant yeast are pretty much interchangeable in recipes (although instant may have somewhat more activity that an equal amount of active dry)

However, your recipe calls for fresh yeast.  The general rule of thumb (referenced here) is to divide the amount of fresh yeast by 3 to convert to active dry or instant yeast.  Your recipe would therefore call for a little more than 1/2 oz of dry.  That would be about 2 packets (or 4 1/2 teaspoons) of active dry or instant.