Hey guys, thanks for your prompt replies!
I’ve seen the one Steve’s suggesting, but not only it’s expensive, also it’s for a RB series (different design) and I’m trying to restore the bike as standard as possible.
The same for CB900 F or CB 1100F, differnt design… thanks Nat
Andy, I’ve also seen the aluminium one which looks actually good enough, but still I’d like to stay original.
About your very kind offer 
: is the cover in magnesium, right?
If so I have to ask to some friend if they’re able to fix it, as far as I know magnesium is quite a difficult material.