I just finished building a 9 inch for a customer's S10 about 2 weeks ago. The very first thing you have to do is get the wheels and tires that you are going to use and get them under the truck in the position that you want them in. Then measure between the mounting surfaces of the wheels so that you will know how wide the rear end needs to be. Then you can start on the rear end.
Narrowing a rear end requires some special tools. You must have a housing fixture to hold everything in line with the differential bearing bore. You also need very good welding skils.
The S10 has about 12 inches of room between the bed side and frame rail. To get a 14 inch wide tire under it you will have to move the frame rails in about 4 or 5 inches at least.