Probability of this being a real mint generated error are zero. These having been coming up for years and not even one has ever been certified as real. Before spending money at a grading service, take it to a local dealer or two.
From the scan it definitely looks like the bicentennial face was machined down. Then the reverse of the 1974 was hollowed out and the face of the bicentennial was dropped in. I saw a show on the History channel that showed a guy making these. He sold them to gift shops as novelty items.
The 1976 was cut and inserted into the 1974 you can see the seam on the bottom and sides of the 1976 side. This is a bad 2 headed half I have seen better.. A lot better. And they should have put both the same year.. still fun to find.
Selling Ryedale sorted USA cents 1.5 each + shipping over 500fv 1.5 each +1/2 shipping If you pick up 1.35 each located MT/ND boarder. after Ryedale sorting they are hand sorted to remove canadian then rechecked with Ryedale to insure all copper and count out $50 FV then placed in cloth bags and sealed with #1 copper wire.