I don't know for sure about LTs, and it might matter what original equipment you still have in, but you might have to (at least) lift one side of the motor I imagine.
The easy way to go about it is tackle it one side at a time by unbolting ONE motor mount and jacking the motor so it leans to one side. Install the header, set the motor back down, bolt the mount back up, and repeat for the other side. Its really not a very difficult operation, just be patient. Make sure to lift the motor by something solid, I'd avoid the oil pan, etc. Also make sure not to pinch/tear/bend anything by leaning the motor too far.
Good luck!