How do you fit a low pressure fuel pump on Nissan CA20?

You don't...

Your system requires 38lbs AT the Pintles. If it is higher that THAT, the usual hard starting (if at all) and high fuel consumption will really annoy you.

I did a switch bypass in my pump (replaced the relay), and I start by turning the key to ignition ON, switch the pump ON for a moment, switch it OFF, then start the vehicle. WHEN IT STARTS I SWITCH THE PUMP ON. WHEN I PARK I SWITCH IT OFF TO DIE.

Bought a PR42 fuel pressure regulator and plumbed it in. It is vacuum-actuated and placed after the filter in-line, which drops the pressure ~50lbs-to-37lbs. Got my mileage back, power curve... ME HAPPY!