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I run an early LC Engr. header and it has the O2 in one runner (#3 or #4 as I recall) and it works fine. No hesitation or stumbling. I think the ECU only adjust A/F mixture a little more than once per second, so unless you are hitting some special resonance point, it won't be able to see a single cylinder's exhaust pulse.

You could always have a flange for the sensor welded onto the main collector pipe and extend the O2 sensor wires down to that point.

Thanks Crawler. That's good info. to have and one less concern. A couple of other findings. The dist. pickup that goes over to the igniter ohms out at 220 ohms (the manual specs 140-180 ohms) Could the higher resistance cause an intermittent miss. In the past when it goes, you lose all ignition. I also mistyped the original post regarding the fuel pressure regulator. I REMOVED the vacuum line to it in order to keep the fuel pressure higher.

'86 4x4 SR5 22re 5" lift 35" BFG's and 5:29 gears.
'05 4x4 DC Tacoma TRD Sport