You have a carbed engine, I presume.
You need to know the max. fuel pressure the carb can hande before the needle blows off the seat, overflowing the float and flooding the carb. Most Holleys like a max F.P. of about 6 PSI. I personally don't trust electric fuel pumps that claim to be "internally" regulated.
Then, you need an adjustable fuel pressure regulator to keep the pressure being delivered by the pump to the carb below that threshold, and an inline liquid filled gauge to measure that pressure so you can set the regulator. Do not by the cheapo "regulator" with the dial on the top.
Install a circuit breaker rated about 5 amps above the max amp draw of the system for your power source, you want switched power to the breaker. From the on side of the breaker to a relay, and the relay lit up again by the on side of the ignition switch, to power up the pump.
As a failsafe, I put a H.D. toggle switch in the ground loop of the fuel pump, giving you the ability to override everything and quickly shut the system down.
If your mechanical pump has failed or is giving you vapor lock problems, it would be easier to solve the problem than it is going to be to do this install right, but I am admittedly anal about this shiznit.