In the earlier post I mentioned the rules not balancing. That was my error. In experimenting with things I had made a minor error with one of the single \quad statements. Apologies. So, at this stage, replacing left=\zerowidthnobreakspace  with left=\quads[3] on the ChapterLeftRule, and doing similarly with right= for the ChapterRightRule, I do achieve something of the kind I am after. I can even go as far as \quads[5] I can see. So maybe I have achieved the desired effect. But it may not be the best way to do it, since I can't control the length of those rules by exact dimensions using this approach. J.