"still would never" means "仍然不" or “还是不”:)

Try to Understanding your example first: When I say 'still would never', I mean something like this: A: 'I would never buy food on the street' ----我永远不会当街买吃的。 B: 'Even if it was cheap?' ----就算便宜也不？ A: 'I still wouldn't buy food on the street' ----（就算是便宜）我还是不会在街上买。 So, in this case, both the two meanings, the 'still would never', in Chinese is '还是永远不会'. The sentance “我还从来不相信他。” sounds a bit weird in Chinese. For me, would like to say 我还从来没相信过他 (= 我从来不曾相信过他) ----I have never believed him Others, I still wouldn't believe him [ever]. ---- 我仍然不会相信他 [从来，任何时候]。 (but whether this sentence might a bit weird in English?) I still never believe him. --- 我还是从来不会相信他。(it seems some problem in logic) --- 我还是永远不会相信他。(this one is right in Chinese) I still don't believe. ---- 我还是不相信。 Yet, I'm not sure... :-)

仍不/仍旧不

just,我从来就（都）不相信他。 I still wouldn't believe him 。（我仍然不会相信他） I still never believe him 。（我还是依然不会相信他）