Please Help

I currently helped a friend of mine install a header that he bought from his friend, I am not sure where his friend got it from but it does not have an EGR Port I am guessing that it is a JDM or european header, WE have it all installed and we just removed all of the EGR components and Fabricated an egr block-off plate, Nor did it have an O2 sensor port, and we are replacing the rest of the exhaust with high flow CATCO cat and A Wide Open Magna-Flow muffler, At this point there is no O2 sensor hooked up, Car cuts down at around 3000 RPM my guess is that it is the the lack of O2 Sensors, Do both sensors need to be hooked up or just one? If only one needs to be hooked up which one Manifold or CAT? Is it Safe to Block off and Remove the EGR system all together? If so What all needs toi be removed besides the EGR, BPT, and plugging up the one vacumn line? Anyone's help or input in this matter would be greatly appreciated.

ALright WE have the exhaust in and the O2 sensor has been moved to after the flex and before the cat on the downpipe, and the second one is in, we then reset the computer and took it for a ride, IT pulled ok through first and then in second somewhere around 5500RPM we got fuel cut, felt like the rev limiter, then after that it cuts down at
2500 RPM feels like it is hitting the rev limiter. EGR system is completely removed The only thing that is left is the Sensor that all of the EGR Vacumn lines goes too, there are three nipples on that sensor, one on the bottom that goes to the throttle body right before the butterfly, then there are two nipples on top, the top nipple is not attached to anything, normally it is attached to the BPT, the second one to the top of the sensor is attached where it normally goes on the intake hose, after the MAF and before the Throttle body. What the heck is going on. why is it cutting at 2500RPM other than because the ECU is cutting fuel. why is the ECU cutting fuel, Is it because the O2 Sensor has been moved so far down stream? or does it have something to do with the EGR system and the Charcoal cannister that is not hooked up, or does it have something to do with the EGR vacumn sensor? Please help???????