where the principle is the same, Rasengan is not as difficult as it's first off human Chakra and second it's perfect shape manipulation of just chakra, where the Bijuu bomb requires a perfect balance of Ying and Yang, (I can't remember something like 4:1 ratio or something).
I don't think he Bijuu bomb was discovered whilst making the Rasengan but the other way around, it's very likely that he got the idea of the Rasengan from seeing the BB, the reason Naruto cant do the Bijuu Bomb is because of the perfect balance and density of the chakra itself, it's designed to be used by the Beasts, they take the Chakra, mix it in their mouth then execute it, now think now much stronger your jaw is compared to your hands, now think how much powerful the beasts jaw must be, Naruto has to do that using his hands and cloak alone, it's much more difficult as the Chakra is much more dense and heavy.
I could be completely wrong, but I think the only way Naruto can do the Bijuu Bomb is if he or his clones go into Sage mode to control it's power, Considering how he sprained his foot in Kyuubi mode when he attacked Kisame, and how he fell from hundred of feet without getting hurt, I'd say Sage mode makes his mode stronger and that additional strength might be enough to control the Kyuubi Chakra and make the Bijuu Bomb.
8:2 actually and not that it's not a good idea but I don't feel he could do both at once or at least hasn't given any indication he can
I feel he needs something better since he can't seem to complete it as he is
@harry: that would work and would be awesome to see but the thing I noticed was that Naruto found out that making a rasengan with his kyuubi cloack active is actually making a tailed beast bomb. I get it that Minato probably derived the rasengan from this. But it doesn't explain why Naruto is capable of making all those variaties on the rasengan but not an ordinary rasengan.
He DID draw inspiration from the tailed beast ball to make Rasengan Bee noted how Naruto nearly fomed a tailed beast ball while making a Rasengan in his chakra cloak