Are Speedmaster elec fuel pumps any good ??

I am assuming that the use of a 750 carb means the engine output would be 500 hp max, probably less. The pump should be sized for the expected HP. Putting a 2000 hp pump on a 500 hp will probably only guarantee one thing: shorter pump life because of all the bypassing the pump will have to do.
A 500 hp engine with correct A/F ratio consumes about 42 gph. The Carter 460X pumps are the most reliable stand alone, external mount pumps, made. More than enough. If the engine makes closer to 400 hp, the Carter 4594 is the best choice, lower output, same reliable design. They are also quite cheap, but not cheap in quality. The simple design eliminates a lot of seals that other brands require which I guess contributes to the cheaper price...