Next time your on ebay also order a $2-3 PCI 80h debug Post card. I know it wouldn't work here, but it's cheap and good thing to have for next time you are debugging.
Can you test that CPU on another board to confirm it works? Is the heatsink warming up at all if you leave it running (Disable fan to check if needed)?
Could be the 8GB memory, try to find a single 2GB stick to test with, this may be the sole/main issue. Pick up a 1GB or 2GB stick from a friend, neighbor, or somewhere in town cheap
Speaker is a must here with no debug card, if you get no beeps with no memory installed then there is a BIOS (messed up) or CPU (Faulty) issue. If you get a single beep with memory installed, then board is posting and you have a graphics issue.
Some old boards like this will not boot with modern graphics cards, some get better with BIOS updated, but since you don't even know what BIOS is on there your "Old R9" may be too new for this board.
Try some old video card, from the P67..... Hmmm.... I guess this would be your original 660
I didn't realize it was launched in 2012 until I looked it up, should be compatible (So BIOS corrupt, CPU faulty, or 8GB is the issue)