From an email on CFSJA list by Hari Rajagopal (formatted and minor editing)

The pump is $30 and believe me, unless you smoke while dealing with volatile chemicals, it's quite safe. Essentially here's the procedure:

1. Go to checkers and get a pump for a 1988 - 1991 GMC/Chevy pickup (1/2 ton, 4wd), get the strainer that goes with it (not incl. in the pump kit) ($5)
2. Get home, flip up rear seat , pull back carpet (1980 and later only) grind off screw heads, pry up the disc shaped cover to access the fuel tank sender get a high pressure air gun or compressed air (available at COMPUSA or other computer stores) and blow ALL debris away
3. Remove + and - wires to the sender
4. Remove the outlet (larger) and the return (smaller) hoses, You can leave the third hose to the left where it is
5. Remove huge ring holding cover and sender plate in place
6. Now, (since there are a couple of different tank shapes this needs to be done) take a stick or a ruler and place in the opening and lower it until you touch the tank bottom. Measure the depth of the tank from the sender plate take the sender assembly lay it flat on the floor, you will find that the strainer at the end of the pickup tube cut off the pickup tube to a length so that the fuel pump,
7. When hooked up via the rubber sleeve provided is an inch or so off the bottom of the tank attach the pump securely (having prepared the wiring as per the sheet that comes with it) to the pickup tube Test for fit by replacing it in the tank and seeing if the plate fits flush with the tank
8. Remove and detach the pump. Drill a 5/32 " hole in the disc and thread the pump wires through it Seal this with a gasoline resistant seal / blob of gasket maker
9. Replace pump and sender assembly and replace lock washer
10. Replace hoses. Now might be a good time to replace them with newer hose if they are spongy and rotted out Tighten clamps
11. Wire the pump with a relay in the engine compartment and triggered by the coil + lead (see the write up on wiring the Aux. fan at the CFSJA site for more details) [Note: You want it to run when the ignition switch is in Run or Start and while the coil + lead is one option, you could also wire to the power lead for the late model Duraspark module which can then power a relay, drawing from the battery to power the pump. Also, don't forget to use a fuse for the pump circuit]

Remember to use a new filter crank it up and enjoy