Thanks a lot @ravenstar68 for your clear explanations 
So it does work very well that way 
(careful in your example for zones.conf the lines name and zonefile shall be identical minus .txt – might be a typo there 3.8..c.b 
)
I am fully aware of the non persistent status of those modifications as I am maintaining my own fork for those tweaks.
Regarding signing and DNSSEC can you please elaborate on what the impact is and eventually advise on how to configure those ?
Thanks a lot again for your help @ravenstar68 and I believe this might come to help in the future for someone in the community running a similar setup.