Use nickel-copper brake lines to make your life easier and your lines corrosion resistant.

https://oppositelock.kinja.com/the-truth-about-copper-brake-lines-1818499200
https://www.copper.org/applications/automotive/brake-tube/brake.html

For flaring, I recommend this flaring tool from Eastwood:
https://www.eastwood.com/eastwood-on-car-flaring-tool-for-3-16-tubing.html

Here are a couple of photos of new rear axle brake lines for my '55 Plymouth.