As your title says, the ruu is your best bet, but I don't think you can run it on a Mac. If you had access to a Windows machine or could install Windows using boot camp, that'd be the way to go. You could also fake it by installing a stock unrooted ROM and the stock recovery, but your bootloader would still be custom.
Yes you can just use the Decrypted.zip Rename it to something simple like RUU.zip put it in your fastboot folder, Open a cmd prompt from that same folder. Relock the bootloader if you are s-on. Put the phone in fastboot usb mode and use these commands