The Saturn I flew in two different versions, the Block I and the Block II. The first four flights of the Saturn I used the Block I version. The Block I only had the S-I Stage as the S-IV Stage was a dummy mock-up. The remaining six launches were of the Block II which included the full S-IV Stage.
One of the most unique features of the Saturn I and its successor the Saturn IB, are the clustered central tanks. In order to save money and development time, they elected to use already created Redstone tanks. These clustered tanks gave the Saturn I a very unique look.