So what we seem to have now is a bit more of a picture of how this router will be used. The age of the OpenWrt version and the security risks have been clearly stated already. And it has also been established that the device in question is not supported by any official current OpenWrt versions, nor is it apparently possible to find a newer release from the original manufacturer.
Additionally, the OpenWrt version is so old that it is unlikely that there would be any meaningful support here from the perspective of people knowing and remembering the nuances of that version (since so much has changed over the years).
With all of that said... the device should theoretically 'just work' as a router, assuming that it is properly configured. Therefore, I would ask @chrisisbd -- is there anything you actually need to do that is not possible with the existing OpenWrt installation on that device? (I am guessing that ssh/telnet, installing packages, etc. is probably not all that necessary if everything is generally working).