Copper exhaust gaskets

Anyone use these with satisfactory results?

I jut put one on the right side of my '69 340, Mr. Gasket PN 7166. It ticks and pffts, leaks like a sieve.


The outside ports of the gasket are rectangular, NOT the truncated angle of the exhaust port. I couldn't see what they looked like to the header...didn't take the header out, just replaced the gasket. It did seem strange the port wasn't the correct shape but, I thought, surely Mr. Gasket knows how to make a gasket.

...maybe not?

Any others with similar OR different experience with this part?

Thanks.