Still not passing emissions check, due to higher than allowable NOx Options

[ActionClaw]

There are more than a few known problems with this car (1995 Toyota Celica ST; 1.8L, 7A-FE) that I need to deal with and I intend to but, right now, I need to focus on passing the emissions test. I'm wondering if some of these other issues may, directly or indirectly, be the cause.

I'm failing the emissions check test due high NOx: 2624.4 with acceptable being around 1072.

• I filled up with premium fuel and drove it to dilute/ burn off fuel injector cleaner that had been added
  (Dont know if this would have made much difference but..)
• I repaired/reinstalled the air hose
  (which was torn, taped/patched,and might just as well not even been there. Air was directly entering, not via the filter or through any sensors.)
• The radiator is filled; car not overheating,
• I removed and thoroughly cleaned the EGR valve
• I removed and thoroughly cleaned the tube from EGR valve to exhaust manifold
• I removed and cleaned the EGR modulator valve (its filter, ports, etc)

It did drop each test and, by the third, it is significantly lower (around 1500) but still not low enough (1072) to pass.

I guess I'll have to replace the catalytic convertor next but is there anything else that could bring it down (almost 500) I might try first ?

A known problem I have is oil leaking into the spark plug wells and I think some might be getting burned.
Regardless, I intend to replace the valve cover gaskets, then oil change and filter, new plugs and wires, etc. but, in the meantime..
Would this (oil burning) problem increase NOx readings?
Would this (oil burning) problem cause the catalytic convertor to fail (which, in turn, would increase NOx readings)?

Thanks

[D-Man]

Remove and clean both O2 sensors. Should have lots of white crusty crap on em; remove. IDFK if it'll get you down 500pts, but it should help. If that dont work, Drive it out to the country (outside city/emissions limits) and have it inspected there

[ActionClaw]

Remove and clean both O2 sensors...

I think one of them is front and center, more or less, behind the radiator but where is a second one?
Hopefully not what I'm thinking of. I noticed some sort of sensor down below (on the exhaust manifold?) in front of the passenger side firewall. Is that it?
Thanks