Just threw a 450lph fuel pump, SS lines, regulator and rail in my car. I want to start it up to check for leaks and what not, maybe drive it around in a bit. Do I have to rewrite the fuel pump since it’s a 450?

Absolutely, that pump draws a lot of amps. You'd be fine to test for leaks and drive around but don't expect it to hold up when you start asking for more pressure out of it.

I wouldn't worry about it, but I would surely do it soon. People have reported the 450 stressing out the stock wiring though.

I turned the key and I didn’t hear any fuel pump noise, which is setting me off. The battery was also pretty dead which could be it but I’ll see soon.
I figure I’ll just do the rewire today. I’m looking into dummy threads about requiring and it talks about PIN 86 of this relay, what relay is it? How do I ask a parts store if they have this type of relay in-stock?

You can use a SPST or SPDT 30 amp Bosch relay for a pump rewire. Both should be available at just about any auto parts stores, or you can order a bunch online for about $1 per relay vs $15 for one.

85 and 86 are the coil terminals, you hook the stock turn on signal to one side and ground the other. Pins 87 and 30 are your high current connections once the coil is activated, allowing straight battery power to go through to the pump. 87a (center pin) in an SPDT relay isn't used on this application, and is common (connected) to pin 30 when the coil is de-energized/off.

So 10-8awg fused battery power to 87, 10-8awg from 30 to fuel pump. Stock pump turn on wire to 85, ground to 86.

Thank you for the help guys.
Also apparently I couldn’t hear the fuel pump just because it’s quiet, definitely have some leaks I need to fix.