I'm doing this same conversion and JimC has helped me with some questions. He asked me to update with my fuel tank part of this install. I ordered the Holley in-tank Sniper fuel pump and when I dropped the tank, it was a mess with horrible rust and corrosion. No real surprises there. It was so bad, that I couldn't get out the fuel level sender on the side of the tank. Instead of attempting to clean the tank up, I got a new one for $200 which also included the cradle for the tank. Not wanting to deal with rust again, I had the tank and cradle coated at Line-X for $130. I don't want to go through replacing the tank anytime in the future.
Before I dropped my tank, I siphoned as much of the fuel out as I could. Then I used the drain in the bottom of the old tank to drain the rest of the gas. I was afraid if I just used the drain, I wouldn't be able to stop the draining of fuel without a mess when It filled a gas can. On the plus side, I discovered that I actually have a working low fuel light!! Never knew that before
The stock opening of the tank is 2" and the Holley pump requires a 3&1/4" opening. I took a 2&1/8" fender washer and tac welded it to the opening of the tank then used a metal 3&1/4" hole saw and cut out the opening. Worked perfectly. Took some time to clean out the inside of the tank but got it done. A second reason I went with a new tank besides the amount of rust, was not having to deal with fumes when welding and cutting the new opening.
Holley fuel pump has three ports. Vent , out and return. I used a NPT fitting to close off the vent since I'll be using the factory vent. Next I'll be running all new fuel lines that were included in the Sniper kit, for the supply and return lines.