Minato obviously had a great understanding of the Tailed Beasts...
The rasengan was modeled after their TBB's ... that should say something alone.
It's my belief that Minato learned more of the Beasts secrets than many believe...
Right before he died with Kushina, he said maintaining the balace of the beasts was important, and thats why Kushina couldn't just take Kurama down with her..
Whether he actually knew about KM, I dont think even Bee know it all..
It seems to me that the So6P is having the Beasts guard something, and they also seem to only give their power to those they deem worthy, ie: Not all jins can corroborate with their beasts to the fullest extent. As we saw with Naruto's most recent fight, They all seem to believe Naruto is one that has proven himself worthy.
Now if we're allowed to tie the Naruto movies into this.. Movie 4 when Naruto went back in time.. Minato, I don't think knew exactly who Naruto was, but was able to tell he had the Kyuubi within him.. His wife had it in her so im sure he could sense it.. and thus When the attack on Konoha took place, It was probably then that all the pieces fell together, and he knew what he had to do.. And having met Naruto and knowing the kind of person he was, felt completely assured of Naruto being able to manage the beast(cause he'd seen it before, no BM or KM but Naruto not being overrun by Kurama).
Soooo after all that, He probably didn't know about KM or BM, aside from the meeting with A & B .. But did know that Naruto would grow to be a strong and diligent man.
the End
