This is not mine, but gets asked a lot.
Get some 1x1 and cut some pieces long enough to weld to the frame and touch the ground. You do this so the front clip of the frame doesn't move front to back once its completely cut.



Once thats done at all 4 corners of it then start cutting them. The 1x1 also acts as a guide for the sawzall to cut a straight line.



Make sure you support the rest of the truck BEFORE you cut so it doesnt drop on ya once the front clip is free from the rest of it. We used scissor jacks (its a bitch i know but it worked hella good.LoL)
Once its all cut now you can lower the rest of the truck down so the front part after the Z hits the ground.


Once its dropped start welding it up and weld some plates on the outside of the frame rails.
If the motor is still in it i would lower it first because there isnt much room at the tunnel for it to go up when the rest of the truck is lowered down. If you plan on doin a bodydrop to it also it would be the best time to do it once the Z is done that way you dont have to do the front part of the frame twice.