[HiFlow5 0]

You did not warp your heads don't worry.

Now you have MAC headers which have individual flange ports. I'm not a fan of these because the header itself will actually warp with heat and not allow your bolt holes to line up, such as you found out.

When I had MAC headers I too elongated the bolt holes and also used a pry bar to get the holes to line up with the heads, what a pain in the ass it was.

As far as the donut exhaust gasket, it's not need at all. Ford uses a ball and socket type exhaust system on the Mustang, so no gaskets are needed excpet for the header to head one only.

Your oil dipstick bolts to the drivers header on the 4th bolt from the front I believe it is. It's just a matter of putting the hanger on the flange and bolting it in.