I'm in the process of dropping a B16A1 into an 89 CRX Si. I bought the wiring adapter kit from HASport, which includes a wire for the second O2 sensor. Now the questions:

My engine only came with half a header, so rather than buy just the bottom half, I purchased a DC Sports 4-1 1 piece for a 94-97 del Sol VTEC (did I at least get that part right?) Nearest I can tell, the header has 1 hole for a sensor. I initially thought the other sensor went after the cat, but now that doesn't seem right... I'm reading about a sensor for a pair of cylinders.

So.... do I need to tap 2 holes for sensors? Or can I just use the 1 sensor hole with 1 sensor and wire it to both pins? Which sensors should I buy? Universal? Brands?

Thanks.