You realize that the 67-72 A body K frames left the factory with a hole there. I have three 67-72 K frames, and they all have it. All three also have a brace welded to the motor mount bracket which yours does not have.
I can't tell from your photo whether your hole is any more ragged than the factory holes.
In any event, like junkyardhero said, nothing was originally mounted there.
Top photo (the dirtiest one) is from my Mom's old 71 Duster 340.
Second one I ran on my 67 Barracuda for several decades (not sure what year K frame it is, but it replaced a slant six K frame in 1991). I replaced it because the Addco front sway bar I used to have on the car broke out the lip on the passenger side where the bar attached.
Last one is what I'm putting in the 67 Barracuda now. Other than being for a 67-72, I don't know where it came from, either. By the way, that's a factory weld on the brace.