Mystery miss on 50 model Ford Custom

[Bullerman]

I ordered a 2.5 to 4 psi pump. I will put it as close to the tank as I can get. Have a new pressure regulator and gauge coming to.
How do I go about cutting the line to install it. I am thinking I will have to drain the tank and take the line loose to cut it and install the pump. Is there an easier way?
Also does it matter which gas cap is on the car. It is not the stock cap. Should it be a non pressurized type cap? Thanks