Kam Lee is the master of the death growl, especially with the style he perfected on the Massacre demos. The early Death demos that feature Kam (Reign Of Terror in particular) are definitley pioneering in the vocal field.
Possessed are one of the first too of course.
Poison from Germany are certainly overlooked, check out the Sons Of Evil demo for Virgin Slaughter's sick death vox.
Xecutioner (pre-Obituary) 1986 demo.
Troy Dixler of Chicago's Devastation intentionally used a growl style too.
Genocide/Repulsion and early Sepultura. Warhammer (U.K.) have proto-"growl vocals". Insanity from the Bay Area also had some hellish vocals too. Ahh, how could I forget the psychos Tschoesi from Messiah and Killjoy from Necrophagia !
Fuck, I might as well let loose- Sarcofago, Nuclear Death, Voor, Vulcano, Samhain (Dnk.), Death Strike/Master. This is all pre-87 anyway BUT from 1987 PARABELLUM. Unbelievable vocals. Majesty (L.A.), Azagthoth (U.K.) (this is more influenced by Napalm Death's vocals). These all being from the metal side of things anyway.