I converted my '57 Custom Tudor from a 6 to a 312 Y-block about 10 years ago. Other than the radiator inlet and outlet being on the opposite sides, the fuel line is also routed on the opposite side of the car from the tank to the pump. All I did to solve that problem was fabricate a steel line from the end of the original fuel line (where it attached to the fuel pump on the 6) and routed the line I fabricated behind the front frame crossmember over to the left side of the engine compartment where your V8 fuel pump will be. If you're a purist... changing the entire line from the tank to the pump is the way to go. Of course... the motor mounts are different... but readily available so no problem there. The transmission gear ratios are different on the trans used with a 6 vs. a V8 if yours is a 3 on the tree... but that's not a big deal.
For the paint issue... any automotive paint supplier that supplies paint to body shops should be able to match the color you need if you bring them a sample (like a headlight ring). I replaced the padded dash on the '57 Fairlane I currently own and a paint supplier was able to match the vinyl dye I needed to a windshield moulding I took them for a sample. They got the color right on the money.
Hope this helps!