on the iBCS part for %install there are several calls to mknod, which can no made as a normal user. building the iBCS devices would be better done on a %post script or telling the user to use MAKDEV.iBCS which is installed
If you do it in the %post, you can't verify the package correctly. At some point, there might be a mechanism in RPM to allow for packaging of special files in a different manner. Until then, we probably won't fix this, or the dev package.