I think what you are asking is:
* Create a VM.
* Test until satisfied.
* Convert the VM to a physical machine.
For converting the VM there are two basic options:
* Convert the VM partition using vboxmanage.
* Copy the VM files.
I have done both.
I have a removable drive caddy to prep new disks.
To convert the VM using vboxmanage:
(The first step is needed only if you are using a dynamic drive.)
vboxmanage clonehd dynamic.vdi fixed.vdi --variant Fixed
vboxmanage convertdd disk_image.vdi disk_image.img --format RAW
I use gparted to create the new partition on a new disk as well as a swap partition.
Then I use dd to copy disk_image.img to the new hard disk partition:
dd if=/path/to/disk_image.img of=/dev/sdX1
The second option requires mounting the VM from the host system which requires bridge networking and NFS. Then I insert my new disk into my removable drive caddy, create the partition, and copy files.
In either case, be sure to check the following on the new disk:
* /etc/fstab
* Delete /etc/udev/rules.d/70-persistent*
You will need a method to boot the system the first time. The Slacwkare DVD should suffice. Then install your preferred boot loader.
I have not provided a detailed check list, but hopefully you get the basic idea.
