The techniques for getting the sounds of those three bands are actually pretty different. Later In Flames especially is completely different in approach to the other two. But you should still be using your diaphragm for both, or else shit's gonna get fucked up. You get more power that way anyhow.
Anyway, if you want a higher growl along the lines of Naglfar, try doing your normal low growl and ascend it until you reach the pitch you want. It's hard to describe, but you can sort of feel the sound moving up your throat as you do it. You're gonna wanna be able to do that anyway, because it sounds cool.
Later In Flames screaming is a lot different from the other growl. You need to use your throat a little bit more to really hit those higher pitches. And it doesn't feel the same as a regular growl. This might sound stupid, but try making a really exagerated "wow" kind of sound, at like a whispering volume level, and get a feel for just getting your vocal chords as high as they can go that way. Then just work on slowly raising the volume, and then push as much air out with your diaphragm somewhat forcefully while making that sound. I know it sounds kind of dumb, but it worked for me.
One other thing, for those really high pitched screams, you're gonna need more volume then you do for the growls. At least I do.
Hope that helps somewhat.
