I am just going to write out the progress/attempts I've made here, on the assumption that some other soul with the same issue(s) happens to come across it.
I managed to get windows 8.1 installed on and exteneral USB by using GimageX and the install.win file (link below)
http://buttur.com/how-to-install-windows...-hard-disk
However the facken BIOS would not allow for booting off of the USB.
So I tried using a windows 8 boot USB, which was just windows to go basically. No joy.
Tried using windows 7 boot usb to force system to look at the external. Waste of time.
Then I decided to disconnect the internal drives from the computer and see how the BIOS felt about that. And it didn't like it one bit. Would not allow me to F9 select boot and eventually ended on a black screen. Ctrl+alt+del seemed pretty useless, and after awhile I just held the power down to turn it off.
Restarted, and this time it did allow me to select a bootpath, and windows even booted up off the external! But crashed at the initialisation screen and auto reboot.
So repeated to selected boot off the external, and made it the distance this time.
It was running slow as heck, felt like I was on an HP all-in-one. But I took the time to updade the drivers on the external OS on the assumption that I'll need to boot into it again. As of yet I have not.
Once all the drivers were installed I plugged the internal drives back in while computer was still live, and...BINGO! drives seen by system. I quickly deleted them, setup a strip drive and am now repeating(more or less) the installation of the OS via the above listed USB method, but to the newly created stripped array. Now waiting for the the files to complete, which is taking an ungodly amount of time because of USB & operation. At least the computer picked up the pace in every other aspect shortly after the 2 SSDs were plugged back in.
All this just to get a stripped OS installation. We'll soon see if Insyde/HP crunch my nuts when I reboot without the external hooked up.
Fingers crossed.