what is the modding of the sensors?? i tell ya hemifever did wonders for mine, i don't have any fancy tunning but you can tell the difference between factory and all 3 tunes on the sct. i would go that route instead of the pcm flash. the headers were a royal pain in the butt, but i learned a trick or two to installing them.
this is for all of you that want to put headers on.......
1. if you have access to a welder then this will be the easy part, on the drivers side and this is only if you didn't get the drop down pipe with the headers, remove your o2 sensor and cut the pipe before the 90 that cuts over to the pass. side. then remove your exhaust manifold, remove the cut pipe from the exhaust manifold and install it on the header, make sure you have the cut pipe pointing in the same direction, i did not do this when i did mine and bolting to the collector was a royal pain. when you install the header you will need an assortment of wrenches and sockets with swivels and extensions, start by the firewall, the first two cylinders are easy the other 3 are a bit difficult, but get the header bolts started on the last 3 cylinders, then torque them all down all thats left on the drivers side it to weld back the pipe you cut in the beginning, reinstall the o2 sensor and your done with the drivers side.
1a. if you don't have a torch you can get a coupling from the autoparts store mine was 2 1/8" id and cut it after the 90 that crosses over to the pass. side. that may be hard to get out unless you think you can cut it in or about the same area as mentioned before. i did mine the hard way, i didn't cut anything and i had one hell of a time trying to bolt the pipe to the header.
2. the pass. side isn't as bad as the drivers side, you don't have to cut the pipe unless you want to but it is not necessary, just remember to start all your header bolts at the same time, once the header meets the head thats it, you will not get the bolts in, take it from me i had to do it twice, i learned from the first time.
one other note, if its possible to take out the plastic fender well that could save you some pain and time. i didn't but it could help.
any other questions about that contact me and i'll answer the best i can.