Naruto and the 4th share many traits, similar hair and eyes to be more precise.
In addition many comments were made to naruto about how a Hogage must be wiling to make the ultimate sacrifices to protect the village. Possibly using your son as the vessel for a demon?
In addition the 4th also sai he wanted Naruto honored as a hero for his sacrifice, and it seems taht he wanted Naruo to succeed because he used a seal taht alllowed the Nine-Tails chakra to be used by Naruto, in stead of totally sealing it.
There is also the fact taht Naruto seems to have an innate talent for learning Jutsu that even having the nine-tails inside him wouldn't effect as much, something that seems in the anime to be more hereditary, some (Rock Lee) having no capacity to learn Ninjutsu and Genjutsu and otehrs (The Sannin/Naruto/Sasuke) seem to be very adept at it.
