Re: electric fuel pump vs. manual fuel pump
Plumbing is as important as the pump itself.
Look at the inlet and outlets, most of the stock and Carter pumps only have a 1/4NPT fitting to connect the lines which they spec as a -6 or 3/8 line. If you think about that you have to ask why? The fuel will only flow at a rate of the smallest orifice which is the hole in the outlet fitting so in reality a 5/16 line is what it's really designed for.
Carbureted Performance engines obviously need more fuel volume to feed the HP output, we have sold thousands of mechanical and electric pumps over the 40 years that we did fuel systems, all our mechanical pumps went through our shop and were drilled and tapped to 3/8 NPT and adapters installed to run -06 AN lines.
Line sizing is very important to maintain proper wall pressure, using a larger line like -08 (1/2") is too large for the fuel pump to maintain constant line pressure and as the line or wall pressure drops volume drops just like your garden hose. Using too large of a line will decrease fuel volume across the needle and seat.
When we were doing fuel systems we had a cam set up on a pair of bearing and we had mounting plates made up for various mechanical pumps so we could run and test them for fuel volume and pressure at various RPM, came in very handing when chasing fuel curve issues.
Be cautious of "Free Flow" numbers we don't have a free flow fuel system on any of our carburetors they all run at 6-8 PSI, in fact Holley has even now fessed up to their false information and they now give you both I believe the Holley Blue that everyone thought made 110 GPH now shows at 6PSI a rating of 72 GPH which is smaller than a properly set up performance mechanical which we found made about 94-98 GPH (but rated at 110). Lots of things affect the flow numbers, line size, 90* cast fittings should never be used on a fuel system, fitting quality we always used nothing but Fragola USA Made fittings and you should never use one of those $5.00 guaranteed to leak chrome plated metal tube dual feed kits from China or a dual feed kit with the 90* fitting to direct the hose to the rear bowl. Use quality parts if you get a leak you may end up with a catastrophic fire... just not worth the small savings.
Make sure that your fuel filter is up to the task.
Do not use rubber fuel line! If you must use rubber line for your connections then get "Fuel Injection High Pressure Line" it designed to run pump gas. NAPA has it.
If anyone's interested I still have one SB Ford 221-302/351 ported to 3/8" in and out it's a Carter M60454 mechanical pump left over on the shelf I'd like to clear it out, $100 I'll ship it free. It has -06 adapters installed in it, sorry no box.