Exhaust Manifold/head problem Troubleshoot (knock)

I have 1998 Jeep Cherokee. Started "knocking" really loud on my way back from the city. I got almost to my house and lost RPM's didn't try and push it. Just pulled over to the side of the road and towed it home.

I have done some reading to try and diagnose the problem. like taking the oil fill cap off and listening to the valve train. Getting under and trying to listen for rod knock. The sound seems to be coming from all around. so...

I took off the valve cover last night and wiggled everything. It all seems to be within the same tolerances. I didn't have anything to measure with just by feel.

After I got it off, I started the engine to see if there was anything not right, thats when I see oil/exhaust blowing out of the exhaust manifold. So obviously it has a crack somewhere in the manifold. My worry is I have a stuck/broken valve, or I am blowing oil past the piston. I am getting a compression tester tonight to check the cylinder.

Any advice on what would be key signs of bad lowerend or upper end?

Any other ways I can for sure know whats wrong. Money is an issue so id like to replace just whats broken. I found a complete head on craigs ready to go for ~450. Id like to stay away from that and just replace the exhaust manifold if possible.

Thanks in advanced.

EDIT: Engine does run, very rough though.

Exhaust Manifold/head problem Troubleshoot (knock)