On my 1990 Z the power antenna was broken in half by the previous owner, and on my previous Z it was disconnected. At the time nobody made a bolt-on part for those who don't want to keep the antenna (as I'm writing this now, I'm still the only one as far as I know). I have had mine installed on my car since 2021 and it has not given me any issues yet.
To start, I took measurements of the original antenna plate and went to make the CAD for it.