from under the car, put the car on tall and stable jackstands
install passanger side first sometimes they slide right in other times you will have to lift the engine alitle.
driversside is where it gets alitle more frustrating, uninstall starter,take apart steering centerlink, unbolt driverside enginemount and tilt engine over towards passangerside as far as you can get it slip header up into that tiny space there is,usualy #1primary pointing at a ridiculus angle upwards behind steeringbox with collector pointing down and alitle in under oilpan when tubes are going up tilt collector up closer to possition, get out from under the car and hold header up in a possition close to right while lovering engine into possition, with engine in place on its mounts again, reinstall starter while you can still move driverside header around alitle,this realy helps, get up again and bolt headers to cylinderhed after that reinstall centerlink and you are bassicly done..
it sounds harder than it realy is just do it all in the right order and they usualy slide right in
i may have forgoten something here but this is the basic way of doing and i have done it many times on my car with simmilardesign headers in the past it and its not all that bad,just takes alitle time and patience
and take out the sparkplugs first it helps if i remember it right
hope it helps alitle