This page will cover the "Z'ing" of the frame on my 84 Silverado.  I cant get the front to set down on the 305/55/20 tires I have for the truck, so I will be Z'ing the front frame rails.  This involves cutting the frame and in this case, raising the section with the crossmember and engine bolted to it so it raises the suspension in relation to the frame.  After you see the pictures, you will understand.
Here is the passenger side frame rail before cutting.
Here is the same side, after I cut it and moved it up 4 inches.
This is the other driver's side, but it shows what I did.  I added 2 piece like this on the outside......
And this is what I did on the inside of the framerail.  The picture doesnt show it, but I added an angled piece on the underside just like on the top.
Here is the front cut and tacked.  You can see the piece of flat stock I welded in for support, since there was not as much room in front to weld like the back.
Here is the passenger side all welded back up.  Looks good, huh?

Well, that is the front just about completed.  I have a few low spots to fill in and grind down.

After all this work, the rockers were STILL not on the ground.  On these trucks there is about a 3 foot section under the cab that hangs down about 1.5 - 2.5 inches.  I had to get rid of this frame section to finally get this truck down sitting on the pavement.
I cut 2.5 inches off the bottom of the frame right as it headed up, at the back of the cab.  I welded in 3 x 3 x 1/4 angle iron.  This was exactly what the truck needed.  It now lays flat out on the rocker panels.
With the extreme drop the turck now has, the transmission was hitting the transmission tunnel, so I had to modify that as well.  No problem!!
Here is where the work pays off.  After all these weeks, the rockers finally plant flat on the garage floor.  Like the rust?  Me neither.  The truck will get all new sheetmetal and paint as soon as the LT1 is wired and plumbed, and can drive on it's own.
I ended up having to buy smaller tires so I could get the front to go down all the way after the "Z".  I had a 305/50/20, which I LOVED, but know I have a 275/45/20.  Here is how close they come to not letting the hood close.