You need a base to build the style on first. You need that fusion of 70s metal with punk rock that made thrash metal, and then you need to make it more "evil" by tuning the guitars down and using death growls. Death growls aren't hard if you know what you're doing (think of Batman's voice in
The Dark Knight and try and sing like that, that's how I learned to do it), and according to some sources were used in ancient Nordic music, not to mention recording techniques can mess with the human voice to make all sorts of messed up sounds.
So basically you need rock music earlier than the late 40s. Which means the context it will emerge in will be different (the Roaring 20s/Great Depression?), the music it will inspire will be different, everything will be different.
Maybe after WWII TTL, you end up with something like death metal in the late 50s. But death metal as we know it is guaranteed to be controversial. The vast majority of the genre revels in lyrics and imagery which is either extremely violent, anti-religious/Satanic, or both. That's not something your "50s badass" types would be listening to IMO (thrash metal, though?), that's music for the fringes of society (maybe a young Charles Manson might like it, so instead of making Beatles ripoff music he becomes an ATL Varg Vikernes). If "Louie Louie" was considered obscene in the 60s, what would society think about something an ATL version of Morbid Angel or Cannibal Corpse in that era? Any record label putting out music like that would be subject to obscenity investigations.
Of course, this era with its hugely divergent history of rock, blues, and jazz might end up with some strange stuff, so maybe the first "death metal" more sounds like Atheist at their most avant-garde and "jazzy" more than anything else. But that's still pretty damn extreme.
Like the genre exists today (with extremely distorted guitars)? No. An extreme music that would be considered the 50s version of death metal? Maybe. After all, rockabilly and 50s rock 'n roll and (especially Like Wray's song "Rumble), and some of the distorted guitar playing of Junior Barnard, and Guitar Slim, were considered pretty extreme for their time. Like death metal is considered violent in most cases (with the exception of maybe some melodic death metal, like Carcass' music), "Rumble" by Link Wray was actually banned from airplay by a significant number of radio stations, due to the fact that it was considered to be music that would incite violence.
Carcass is a very bad example to use, if only for their name. But even Heartwork and Swansong would be considered violent to anyone who doesn't know better. Link Wray was indeed pretty extreme for his era though.