Balls on.
Sell those heads, they are worthless. You gain so little, it's not even worth the money changing out the gaskets. The money is much better spent porting your stock heads. If you port out the stock E7s vs. porting out the stock Cobra heads, the Cobra heads produce between 1 and 3 more hp at the crank. If you really can't afford a better set of heads, and you can't afford to port your stock ones, go to a junk yard and pick up a set of heads off a Ford Explorer. They perform much better than the Cobra heads.
If you put those Cobra heads on your GT as it is right now, you would most likely pick up nothing.
Kurt