Answers to previous questions regarding this sensor and failing CO Test on the referenced vehicle proved very helpful. However, for future reference there is only one O2 sensor on this vehicle located in the left exhaust manifold where the right exhaust bank joins (no dual exhausts on this model). Purchased OEM O2 sensor for $67 and installed myself (1 hour job). Vehicle passed retest in the CO and other categories with "flying colors" with very low readings. Also increased gas mileage significantly. Above info just in case anyone else has similar problems.
O2 sensor--1986 Nissan 300 zx on 1990 Nissan 300ZX
Thanks for the update!