Hello all! I need your collective guidance on a smog question on my 242

Picked up a sweet 242 with a B21F Kjet/Lamda Sond system on it. The car passed a California smog check about 12 months ago, but failed Nox emissions after purchase 3 mos ago. The car did very well on HC% and CO%, but was almost double the allowable on NOx before all this tune up work. I've done the following tune up parts already

New Plugs
New Plug Wires
New Cap
New Rotor
New Oil Filter/Oil
New Air filter
New Injector Seals
New Fuel Filter
New Upper and Lower AAR hoses
New Engine/Trans Mounts
New Exhaust gasket between header and down pipe.

Car had a headgasket and timing belt done before I bought it (claimed new head as well, but doubtful. I'm guessing it was just cleaned up). Car also has a receipt for a new catalytic converter, welded in....

I've ultrasonically cleaned the injectors.
I've set the timing on the car (10* BTDC at idle, spec is 8* +/- 2*).
I've verified the Cold Start Valve (CSV) functions (that means my thermotime switch functions as well).
I've verified the Auxillary Air Valve works (ohm test and flash light test).

The car has a lumpy idle but revs fine, and drives fine... just rough at idle.

When I got the car, I noticed that the 1-wire 02 sensor was disconnected, and that the wiring in the engine harness had been patched/repaired etc. This tells me that the Lamda Sond system is not doing anything at the moment. Frankly, I'm not sure where it gets plugged into either.

It also sounds (and a smog guy commented) that there is an exhaust leak. I replaced the downpipe to header gasket, but have found a crack on the flange. I purchased some exhaust epoxy to seal the crack, hoping this is the cause of the leak.

Questions:
1) Can an exhaust leak before the catalytic converter throw off Nox readings?
2) Does the disconnected lamda sond have an affect on NOx?
3) Do i bother hooking up the lamda sond? or remove the O2 and plug the bung to pass visual?
4) Sources of high Nox? Read lean mixture/retarded timing/Hot motor/carbon deposits can be the cause

I really need to get this thing through smog. I've dumped a bunch of other money into new suspension,steering,etc for it already.

Your advice is very much appreciated!!
-Aaron