I have a computer with multiple hard drives. I originally installed Windows 8.1 x86 and recently installed Windows 8.1 x64 onto another hard drive in the same machine. How can I copy or move files and apps from the old x86 to the newer x64. I am trying to avoid having to re-install all of my apps and setup everything back up all over again. How can I avoid this headache?

You can copy data but you cannot copy the system files they are VERY different.  You may be able to move apps on a case by case basis but since you have not told us which you have it would only be a guess.