Head Gasket leak/hissing noise

Earlier today I got home and turned my stang off. I saw smoke coming from the hood, so I popped the hood and saw smoke coming from underneath the passenger side valve cover/head gasket area. I also heard a hissing noise coming from this area (sounded like pressure being relieved). I noticed a small amount of antifreeze on top of the passenger side "Ford Motorsport" valve cover. Head gasket leak perhaps?

I've checked the oil and it seems fine. It is running Royal Purple 20W50 oil. It's a 1990 5.0.

I will check along side the intake coolant pipe to see if it leaked. What concerns me is the hissing noise coming from this area after turning off the car. It sounds like a radiator blowing off pressure.

There is also oil leaking from either the head gasket or the valve cover which is running down to the header causing smoke.

I don't know if the hissing is coming from the coolant pipe next to the manifold, or from the apparent gap in the valve cover or head gasket.

The engine runs fine, no known difference in the way it runs today and last week.