To convert a 2WD cab to 4WD you need to cut the floor out of a donor cab, or your existing cab you are replacing, this goes back under the seat portion for the 4WD.
If you need references here is a link for the different humps.
http://forum.73-87chevytrucks.com/smforum/index.php?topic=11838.0First cut the floor out of the donor
![](http://www.73-87chevytrucks.com/techinfo/2WDto4WD/cut_floor1.jpg)
Once removed drop it in over your existing floor and make sure it is aligned.
![](http://www.73-87chevytrucks.com/techinfo/2WDto4WD/cut_floor2.jpg)
![](http://www.73-87chevytrucks.com/techinfo/2WDto4WD/cut_floor3.jpg)
![](http://www.73-87chevytrucks.com/techinfo/2WDto4WD/cut_floor4.jpg)
![](http://www.73-87chevytrucks.com/techinfo/2WDto4WD/cut_floor5.jpg)
Mark the perimiter of the cut out floor and then measure in about 2 inches and mark another line inside what you have already marked.
Break out your favorite cutter: cutoff wheel, plasma cutter, sawzall and go to town.
![](http://www.73-87chevytrucks.com/techinfo/2WDto4WD/cut_floor6.jpg)
At this point you can secure the floor with 1/4" self tapping screws and used 2 sided butyl tape or weld it in.
![](http://www.73-87chevytrucks.com/techinfo/2WDto4WD/cut_floor7.jpg)
![](http://www.73-87chevytrucks.com/techinfo/2WDto4WD/cut_floor8.jpg)