I do my cbr->epub conversions using Kindle Comic Converter.
Contrary to the name, it targets many devices, not just Kindle.
The home page is
https://github.com/ciromattia/kcc and the Mobileread sticky thread is here
https://www.mobileread.com/forums/sh...d.php?t=207461
The maintainer (AcidWeb I believe) is active on Mobileread.
Edit: I believe there might even be a Calibre plugin. I don't use Calibre though, so I only have experience with the standalone version.