Using an eq analyzer, look for the highest peak, that's the strongest frequency and therefore the note. Each subsequent peak after that are overtones/harmonics. Unless these screams don't appear to have a peak frequency, then idk.

Experiment with different mics. You can sometimes get some pretty good stuff from an SM58.

Layer up the vocals , and experiment with different EQs on different layers. The Marilyn Manson way!

Compress the living shit out of it.

You can also get some pretty cool effects by distorting the scream slightly, either after you've recorded, or using more natural distortion from your pre-amp.

metal screamers

metal screamers are piece of cake dude.

a good dynamic mic sounds great. good condensers sounds great.
tube condensers sound the best but pricey.
you can make pro recordings with just about anything now of days
grab a low level from him start with a dry signal.

as far as eq, use a tight Q setting 160-220 ish to get some chestness

3200- 4200 for your higher mids.

auxiliary bus over to a delay. use a slight delay not much feedback. in the back round, it will make it flow together better.
re verbs your choice., if you do, again aux bus verb in the center
compress it

have him scream clearly into the mic. and do it in an open room not a small chamber

vocals are mono , pan 0

http://cdmasternow.com

One other thing to add is make sure you use a mic that can withstand the db's created with voices like that. Distortion of the mic diaphram is not a pretty sound nor is it a usable one even in this case. Dynamics are good and condensers that'll take up to 140dbs work also. Sweet or delicate sounding mics aint gonna work.

I've never heard a vocalist reach this 140db that everyone worries about.

Hell, when I recorded vocals at my old College studio, we tried a whole bunch of mics and I swear I could hear the mics laughing at me because I was zero challenge for them, and I'm a hella loud vocalist.
Worry less, just be conservative with the gain.