About the chevy small block fuel pump
The fuel pump on a chevy small block is located on the passenger side front corner of the engine. It is immediately in front of the motor mount. To demonstrate how to change the chevy small block fuel pump I am going to remove and replace the fuel pump on a seized chevy 305 I recently (May 2007) removed from my truck.
Chevy small block fuel pumps have not changed much in decades, at least for the period between the mid fifties thru the mid eighties. For the classic car engine, there was typically a single gas supply line. Most of the differences in chevy small block fuel pumps over the years are in the fittings and the assembly of the body of the fuel pump. Chevy small block fuel pumps in the fifties and early sixties were completely rebuildable, whereas now they are a throwaway item. They should go to recycling however.
I did it Myself!With Tools and Instruction
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For newer cars with a vapor return, there were 3 lines. One is the gas supply line, one is the vapor line and the third is the pressurized outlet. The supply lines in each case are joined to the fuel pump inlet(s) with a rubber fuel hose and retained with small clamps. The pressure side or outlet line between the fuel pump and the carburator is metal with flare nut fittings on each end. To change the fuel pump you don't need to undo the flare nut fitting at the carburator, only at the fuel pump.
The fuel pump arm on the 
backside of the fuel pump is driven by a push rod. The other end of the push rod rides on a special cam shaft lobe simply shaped like an off centered circle. This push rod will fall or slide down behind the fuel pump backing plate when you remove the fuel pump. This presents a special challenge when you are trying to install the replacement pump. I'll show you how to make installing it a lot easier.
Remove the chevy small block fuel pump
Use a 5/8" "line" wrench to remove the metal fuel line. On most classic chevy small block fuel pumps the line wrench you use to remove the flare nut would be 1/2". If the motor has recently been running the fuel line may be pressurized with fuel. Be prepared for this fuel to leak. Wrap a rag around the wrench and flare nut to capture the leaking fuel. Do not smoke and be sure no one else in the shop is welding or using a nearby flame.
Don't bend the metal line, even slightly. Once the flare nut is removed and you can slide it back, you do not need to pull the metal line out of the fuel pump fitting. If you force it to come out it could bend and you will have a tough time starting the threads when it is time to reinstall the new fuel pump.
Remove the rubber fuel line from the pump and plug the fuel line with something to prevent the line from leaking fuel. I usually use the butt end of a drill bit. The check valves in the fuel pump, provided they are working should prevent the fuel pump from draining any fuel onto the floor. The fuel supply line can be 5/16" or 3/8".
Use a socket, ratchet and extension to remove the fuel pump flange bolts. The bolts on this fuel pump happen to be 7/16". It's not uncommon for someone to replace the factory bolts so you could run into fuel pump bolts with a 9/16" head. The bolt size is a 3/8" course thread. You should not remove one bolt entirely, then the other. Loosen both bolts, then alternate between them until they are out.
Notice the picture in the fourth paragraph where I show the fuel pump push rod has slid down behind the fuel pump backing plate. Next you need to remove the fuel pump backing plate so you can remove the fuel pump push rod. Use a 3/8" socket and ratchet. Use an extension of the appropriate length.
Install the new chevy small block fuel pump.
Clean the parts. Use a thick grease to lightly coat 
the fuel pump push rod. The grease is going to prevent the fuel pump push rod from falling out when you remove your hold on it. I used a fair amount in this photo just for illustration, but you really don't need that much. Wipe out the fuel pump push rod cavity with a rag to remove any excess oil. Insert the push rod into the hole until it contacts the cam shaft and will not go any further. Do not use a hammer to force it, it will not go any further.
Clean any remaining gasket from the engine block and 
the fuel pump backing plate. Glue the new gasket to the back of the fuel pump backing plate. I usually use "yellow death" or weatherstripping adhesive. Use a solvent and a rag to be sure all parts are grease free before glueing the new gasket in place. Use a very thin smear of automotive silicone on the gasket surface after glueing the gasket in place. Place the fuel pump backing plate in place on the engine block and start all 4 of the bolts in their respective holes. Tighten the 2 small ones at the bottom of the fuel pump backing plate, then remove the 2 fuel pump bolts.
If you tighten each bolt after putting it in place, by the time you get to the others you may find that the bolts cannot be started in the threaded bolt holes because the fuel pump backing plate is not properly aligned. Starting all the bolts before you tighten any of them will ensure you will not have any difficulty when installing the fuel pump flange bolts.
Glue the new gasket inplace on the fuel pump, and then put a very thin smear of automotive silicone on the gasket. Put the fuel pump bolts in the fuel pump flange bolt holes. Put a spot of grease on the end of the fuel pump arm and put the fuel pump in place. Make sure the metal fuel line is aligned with the fuel pump fitting. Hold the pump in place with one hand while starting the threads on each of the fuel pump bolts. While holding the pump in place be sure to hold it upright, preventing the fuel pump arm from slipping to the side of the end of the fuel pump push rod. Once both fuel pump bolts are started, alternate between them, tightening each a couple of turns until they are both snug. Tighten them down to approximately 25 ft/lbs. You should see a fine bead of silicone squeeze out from around the fuel pump and fuel pump backing plate.
Replace the rubber fuel lines and start the flare nut by hand. You may need to wiggle the metal line to get the flare nut threads to start. If you push the fuel line straight into the fule pump fitting it will center itself, making the flare nut easier to start in the fitting. Do not attempt to start the flare nut using a wrench. You could easily cross thread the fitting. There may be some tension on the fuel line that makes this a bit difficult to work though, but in any event do not bend the line. You may need to flex it slightly if it does not line up wth the fuel pump fitting however.
Start the engine. There should be enough residual fuel in the injectors or the carburator to start the engine.