looking at the e1c63x64.inf, the e1c63x64.sys is included, please share the model of your Intel(R) network adapter so we can further check on this one. Have you tried to run the installer file on the Win8.1 machine and see if it will proceed with the installation? another method is to try the setupBD.exe found in the extracted folders (usual path = apps\setup\setupbd\win64)
Did you try using 3rd party driver update tool? It will start an automatic detection of all drivers and find the updates and problems then update or fix them quickly and easily.
If needed, use totally free tool DriveTheLife for a try.