First off, great story.  You've probably heard it all before.
Overview:
Ranma as Captain America
Kodachi as Iron Man
Akane as Thor
Mousse as Daredevil
Ryouga as Hulk

At first I was trying to decide who the time-manipulator was: Kang or 
Immortus (this is a crux point, by the way, since while Kang becomes 
Immortus, not all Kangs become Immortus.  Avengers Forever, baby!).
Boy, oh boy, have you caught me at a good time for an Avengers/Ranma fusion.  
I've just read the ESSENTIAL AVENGERS and MARVELS, as well as quite a bit of 
Avernger's by Busiek.
Ryouga as Hulk, how obvious is that??  Mousse as Daredevil, again, how 
obvious is that?  But a GODDESS OF THUNDER???  Obviously Odin has been 
getting ideas from EARTH-X.  But it would make for an interesting personality 
thing for Akane when she finally figures out that, hey, Thor is supposed to 
be male.  And then along came the Enchantress (whom I fell in love with in 
WORLDENGINE) . . .  And let's not even think about Sif.  Though i do look 
forward to seeing the Frog of Thunder again.

Since I am also making an anime-comic fusion (though not characters but 
rather archetypes . . . God, don't get me started cause I'll never stop), I 
do have a few suggestions, obvious ones and hopefully not so obvious ones:
"Copycat" Ken as The Taskmaster
Eat Man (by god, that name cracks me up something fierce) as Crusher Creel 
only with slightly modified powers . . .
Ok, ok, bear with me here but . . . 
Azusa Shiratori as THE COLLECTOR
Tatewaki Kuno of a parallel universe as Proctor
Hmm . . .
Nabiki as Loki?  But then why would they each be reincarnated as sisters?  
Makes you wonder what goes on in that crazy head of Odin's.

Ok, ok, here's another crazy one:
Minky Momo as NIGHTMARE

Keel Lorenze as Korvac?
Who better to be the Mandarin than Nakago?
Ah, and DBZ's Cell as Ultron!
Herb as Baron Zemo.

Ok, here's some other things.  Nit-picks, really.

The reason that Hulk never really quite figured out that he was RBB (the 
stupid child-like tantrum throwing one anyway) was because he was all of 
RBB's suppressed rage at the world in a seperate personality, long before the 
gamma bomb (Let's count the Hulk's personalities!  Bruce Banner, Hulk SMASH 
Hulk, Mr. Fixit Hulk, the combined Bruce-Hulk, Maestro, Surly Hulk without 
Bruce, Bruce SMASH Bruce, Mindless Hulk (thouth that may be a part of Smash 
Hulk), and . . .umm . . . I think there's more but I'm not sure).  Brucey had 
one screwed up life.  Now Ryouga does not supress his rage, and I doubt that 
the "trauma" of the Gamma Blast was enough to fracture his mind.  God help 
you if you go the Byrne route, by the way, for the rest of us won't.  

One wonder's if a nationistic symbol of Japan during WW2 would react to 
"today's" Japan.  Probably the same way that Cap SHOULD have reacted to HUAC 
and McCarthyism, though less intense.
And don't you think, in terms of personality, that Hawkeye would have been 
better for Ranma than Cap?  Never mind . . . 
So until Shampoo says, "By the Hoary Hosts of Hoggoth" make mine DB.
EXSELSIOR!

-Murmur the Fallen
As seen in Supergirl #33, but without the crappy haircut