How do you do the early death metal growl?

I'm listening to Death and Possessed and I'm thinking to myself, "how did they do that?" The early death metal growl or scream, I can't really define it, is kinda awkward to do and is completely different from the death growl now. I have absolutely no idea how to do it. To do the Mille Petrozza scream is really easy since it's a literal scream and the regular death metal growl is easier to pull off or fake. I just need to know how Chuck Schuldiner and Jeff Becerra do the early death growl.