Depending on what motherboard/bios you have...
You could shrink your windows hard disk, then restart and go to the bios - select "Legacy" or "Legacy first" (over uEFI)
Insert any linux boot CD or USB and you will have a free portion that Linux can be installed to (the space you opened up when shrinking).
If it works, then changing that one option in the bios would have the system booting to Windows or Linux based on uEFI or Legacy.
Tambien tengo risers y muchas placas GPU que quedan si estas en buenos aires. Te los vendo.