I appreciate it, but it looks like the magnet link is formatted incorrectly... EDIT: nvm, I saw that you changed your post. Thanks!
Got it to work. D/Ling now. A quick question; when you extracted your product key, did you use it to install, or just to activate?
Just to activate. Use the generic ARM product key (included inside READ ME.txt) during installation. Once it installs, go into settings, then Activate. It'll ask you for your product key. Enter your own product key.
How did you manage to boot from USB? I used UltraISO and just replaced the WIMs, saving back the ISO under a different name, then I used Rufus, as I always do when making bootable USB drives. Still, it's not booting with the usual Power+VolDown, it just flashes for a second and then boots normally. I already installed 8.1 through Windows, but this tiny issue with boot has been bothering me...
I was able to boot from USB. I used 7zip to extract the original ISO to a folder named "\Windows 8.1 RT" on my desktop. I copied boot.wim/install.wim to a folder within C:\ and then added drivers using DISM. I then copied and overwrote boot.wim/inistall.wim back to their directory within the "\Windows 8.1 RT" folder on my desktop. Finally, I copied everything within "\Windows 8.1 RT" to my USB Flash drive. I was able to boot to it with no issues. Held down the volume down button. Held down the power button for like 5 secs. Then I let go of the volume down button once the Surface powered on and I saw activity on my flash drive (LED light). ....make sure that your flash drive is formatted using FAT32. I believe that makes a difference. You can't use NTFS when booting off of it for an installation.
This is most likely the issue he's seeing. UEFI boot like the Surface has does not support NTFS; it requires FAT32.
To boot from USB without the key combination: Go to PC Settings, Update and recovery, Recovery, Advanced Startup - Restart now. Then select "Use a device - USB Drive".