Sometimes lifting the motor helps. It comes down to what you have available at your disposal.

 

Which side? My driver's side I had to remove the steering shaft and then the headers slipped in from the top with ease. The passenger side went up through the bottom. This was on a 4WD.

 

this should work for most trucks unless you have some really saggy motor mounts they may touch on the passenger side frame

 

On the GMT-800 2wd trucks I install from the bottom although the pass side can install from the top. I remove both heat shields for extra clearance and they do not get reinstalled. I pull the bolt out of the steering shaft to aid in bolt/gasket install. It's a good time to install spark plugs while the shaft is out of the way. With Speed Engineering headers the drivers heat shield has to be removed for the o2 sensors clearance. That o2 is super tight to the floor pan without the heat shield installed. You could trim out the shield for o2 clearance if you are **** about keeping the heat shield.

Get the ICT Billet header bolts as they are zinc plated and will not corrode inside the head. Always use new GM exhaust manifold gaskets or the equivalent MAHLE MS16124 gaskets to save some money. Don't use the cheap bi-metal gaskets that come with the headers.