Engine knocking sound, what could it be?, 73 2.0L Options

[highways]

Hey guys,

So I've got my project driving again but I'm concerned about a knocking sound. It seems to come from the top center of the engine (like under the throttle body or that general area). You don't hear it very much when listening underneath the car. When the car is cold- for the first 10-20 seconds of running it sounds normal. Then the knocking starts as it heats up. It seems like it possibly gets a little worse as the engine get's hotter.

The engines history- 108,000 miles. It sat for five years. I sprayed WD40 and marvel mystery oil into the spark plug holes. It cranked over and started just fine. Drained the oil, replaced. Redid the vacuum lines. I'm 95% certain I got everythintg back on there but there is the possibility for error. Redid the fuel system. Checked the new spark plugs after 10 minutes of running- two spark plugs were found to be blackened. The other two were clean. Timing is uncertain and only 'roughed in' at this point. The engine does 'hunt' and occilate when idleing. It goes between 800-1,300 RPM's.

I need some help diagnosing this knocking sound inorder to figure out if it's something to worry about or just a normal engine sound. It's hard to tell. Any thoughts?