Stainless lines are expensive but you won't need to replace them, don't rust, very strong, etc.
1. Put the mechanical pump on ebay, block your hole
2. By an electric pusher ala Holley red/blue (regulate as required)
- this are pusher pumps. I custom made brackets for both of mine
(ones dedicated to NOS) and mounted it just below the tank line exit.
3. Ran my lines down the frame rails and through the trans mount using
a bulkhead fitting, up the back of the firewall where both regulators
are mounted as close to the carb as I could, and then to flex #6 to carb
and flex #4 to NOS Solenoids.
It's tricky with dual exhaust through the rear valance but it worked out sweet. Use A/N fittings....don't even go for that inverted 45 flare of old. Best flare tool for me is the Rigid tool about $100 bucks. (I did all my own 3/8 stainless brake lines in A/N as well so it was worth the investment).
As far as size versus need. 3/8 lines properly motivated is plenty for just about anything you'll run on the street. e.g.
WOT/full power fuel consumption for a beefy street machine will be ~ .5lbs of fuel per Horse Power Per hour. Gasoline weighs in at about 6lbs/gallon. So for a 450HP engine you'll need about 37 Gallons of fuel per hour. A Holley 'Blue' delivers 110 Gallons per hour. at ~ half it's rated pressure of 14 let's guestimate it'll give you half the volume...still leaves 18 gallons/hour of margin ~50% derated from the need..so we could be off as much as 50% and still meet the need.
Besides,
1. Who drives WOT @ full power for an hour.
2. You have a built in capacitor with the float bowl.