Header Installation/ Two O2 Sensors???, What And Why And Of Course How? Options

[ColdRedRush]

so i recently took my baby into the shop where i work and took off that beautiful heat shield that covers the exhaust manifold thats been on there for 15 years. and discovered that my exhaust manifold is cracked in 7 different places and thats just on the visible part of it, no telling what it looks like underneath. to any extent ive decided that its time to get the header of my dreams. one small problem... there are two O2 sensors, one on the manifold and one after the cat. or just before it i dont recall. every header ive found through craigslist or ebay comes in 2 pieces, with only one O2 sensor port. now im no master mechanic but i do know you need an O2 sensor. the question being...do you need 2??? can anyone makes some recommendations or comments on the matter for me please greatly appreciated... thanks and much celi-love.
-charlie (ColdRedRush)