I thought you'd like Mortuary Drape and Master's Hammer as they have a very old school sound. Did you not enjoy Root?
Have you tried the Greek black metal scene? A of the stuff has quite a bit of a heavy metal sound to it that I think you might like.
I'll just name the most popular 3 because you've been given quite a lot to get through.
Rotting Christ - Thy Mighty Contract (if you like it Non Serviam is also worthy)
Varathron - His Majesty at the Swamp (if you like it Walpurgisnacht is also worthy. In fact I may be in the minority that prefers it)
Necromantia - Scarlet Evil Witching Black (if you like it Crossing the Fiery Path is worthy and the Ancient Pride EP has a Manowar cover who I know you like)
Also, Lovecraft mentioned it but I'll second Poison - Into the Abyss incase you missed it. Some of the best 80s death/thrash with a very old school sound