HSSS427: I hate to butt in again, but my car is also an ERA with slip-fit primaries. These may fit loosely when cold, but swell when hot to seal the joint. One problem that is created when a header leaks is the header and head errode around the exhaust ports under the gasket, ensuring that a new gasket will leak. I had to mill the exhaust-header mounting face on both the head and headers to fix the leak. You already know how The backfire on my engine was fixed by pinning the cracks in the old tunnel-port heads.
