1982 Nissan 280Z 280zx starts up fine runs amazingly. But fa

Engine Mechanical problem
1982 Nissan 280Z 6 cyl Two Wheel Drive Manual xxxxxx miles

original results were Hc 6.43 (passable is 3) Co 99.61 (passable 25) and nox.72 (passable 3.5). So I replaced the cat with a california cat, all spark plugs (the ones I took out were gapped.2 instead of.45) changed all plug wires, distributor cap and rotor, upgraded the stock filter (can not find stock filters for it) with a spectre performance filter (largest and most breathable filter available) and kept it in the stock spot, and poured in a little NoS fuel addative that cleans the system out and lowers HC and CO readings. Took it back, drove it around for a few minuets (maybe 15) to warm it up, took it in at running temp (dead center on the temp gauge) and it failed with HC 6.24 CO 124.45 and blew nox away with.07. I used the Napa head/gasket test for the radiator. Blue-> yellow= leaking had/gasket. Mine turned green. Noticed the radiator fluid had been sucked up to the bottom of the tester so I retsted it and got the same results, but again had radiator fluid sucked up to the tester. The exost does not smell of radiator fluid, I have no error codes when I press the computer button on the dash and no idiot lights, and the oil looks and smells clean with no bubbles. Also did a compression test- 5/6 cylinders are at 160-170 and one was 140-150 (from what I read they should be 160+/-5%) My on dash oil pressure gauge sits at about 50psi at idle but varies up to i'd say about 60. With the car out of gear revving up to 3k rpm the oil pressure goes to 60-70 and the cap is around 100. The vehicle drives great, has no lack of power or pickup in speed, does not sputter at low or high rpm, and has no problem going up to and past 5k rpm As suggested by the emissions tester I tried to take it to a mechanic shop but I was just told the vehicle is too old and they cannot do anything with it. Misc other things I have done are replace the radiator with a factory new radiator and replace the fuel cap with a junkyard cap (was sold to me without one and new parts are very difficult to find)