Headers

take the starter off, and unbolt the engine from the motor mounts. leave the brackets (they are the ones with the 4 bolts) on your engine, but unbolt either from the top side or bottom side of your motor mount (the rubber type one with the larger nut on top and bottom). i unbolted from the bottom so when you lower the engine afterwards you can guide it back into place if needed.
you will need to raise the engine, either with a hoist, or putting a jack underneath and jacking up under the oil pan. i did the oil pan method with a piece of wood between the jack and pan, since my hoist was occupied elsewhere, but just be gentle if you go that route.
you don't need to unbolt your tranny but maybe just loosen the mounts so you have a little bit of play without stressing the tranny crossmember.
make sure the car is high off the ground, because you will need to guide the headers in from underneath. the passenger side is simple to get in, but the drivers side you will probably want to get help, have someone pull from above while you try to guide it in from underneath.
once they are in you will need to variate from lowering the engine back in, to moving the headers around, to get them in place.
to get the starter back in you will want to have your headers unbolted, and your steering still taken apart. you may have to pry it in a bit, as its a tight fit.
then bolt the headers tight with gaskets, and put your steering back together. dont forget to make sure if your steering wheel is all the way left, to have your spindles turned to the left, so your pitman arm will go back on using the correct grooves (if you took it off).

hope that makes sense and helps