You would not want to install -dev packages on a Conduit, since usually these are for building objects, and development tools will not fit. You must cross compile if you are to compile objects.
The list of pre-built packages is referenced on this page:
http://www.multitech.net/developer/downloads/
Look for pre-built packages. If you follow the links, you will find both MTCAP and MTCDT hardware at various levels.
Installation instructions are here:
http://www.multitech.net/developer/software/mlinux/using-mlinux/opkg-package-manager/
If none of the packages are what you want, you will need to investigate open-embedded, and build what you want using our tools:
The title of this is building images, but you can build individual packages as well with the bitbake command:
http://www.multitech.net/developer/software/mlinux/mlinux-building-images/
You could then copy the files in build/tmp/deploy/ipk onto an HTML server of your own, and reconfigure /etc/opkg/mlinux-feed.conf to point at your packages.