I installed the Virtualbox guest additions in beta 8 recently, but there wasn't any need for kernel-headers or kernel-dev, etc. If I remember correctly, I simply choose Insert Guest Additions from the VM Devices menu and entered the root password. After the next restart I was able set screen resolutions. Did you try without installing kernel-headers?
Just downloaded the CD today https://www.oracle.com/technetwork/server-storage/linux/downloads/linux-beta-4409163.html . Workstation 8 has kernel-headers installed by default. Might be kernel-devel might be not required. I just added it just in case. Surely it's failing that missing package elfutils-libelf-devel. I was able to proceed only after installing elfutils-libelf-devel manually.