I've been doing the method below for Windows 7/8/8.1 keys on machines that haven't had an install of 10 on them yet.
-Install Windows 10 to the correct version that you have a key for saying "I don't have a key"
-Once you get to the desktop after the setup open "About" and it will mention that Windows isn't activated.
-Click on "Change Key" and enter the Windows 7/8/8.1 key and Microsoft will activate the copy of Windows 10 as long as you selected the right version to the key you have.
The above is what I'm worried will stop working soon
Intel i7-7700, MSI Trident, 32GB DDR4 2133mhz, Geforce 1060GTX, and Samsung Evo 1TB.