Brake lines use 45 degree flares. You can get a flaring tool from your local O'Reilly's, Rent for 2 days or purchase. Link It'll make the proper double flares on multiple sizes of tubing. Most lines on an AD truck are 1/4", with possibly a 5/16" one. I'll bet the earlier trucks were the same. I bought a coil of copper-nickel brake line which is easy to bend and flare.

Kevin
1951 Chevy 3100 work truck
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1929 Ford pickup restored from the ground up. | 1929 Ford Special Coupe (First car)
Busting rust since the mid-60's
If you're smart enough to take it apart, you darn well better be smart enough to put it back together.