It's been a long time but I think Savage Sword (and later, King Conan) are basically fully separate titles. I think the regular 'Conan the Barbarian' is a single story in and of itself.
The slightly slimmer look with the goofy front-horns helmet is definitely young Conan. He'll change looks throughout the Marvel run. You're looking at 1970s Marvel Conan. I think the other BFS Conan is more like.. late 80s, early 90s Conan. Same comic, though. Just close to like issue 250 than issue 2.
Edit: I flipped through some issues and I was wrong. Looks like the original BFS Conan is based more on around Conan the Barbarian 58-60ish. Which is also when Belit first appears.