Sorry, I thought you had a 3/4 ton shortened to a 1/2 ton.
My answer is still to to use the size line that came with the original brake system if that's what you still have under the truck..

Grigg

•1951 GMC 250 in the Project Journals
•1948 Chevrolet 6400 - Detroit Diesel 4-53T - Roadranger 10 speed overdrive - 4 wheel disc brakes
•1952 Chevrolet 3800 pickup
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"First, get a clear notion of what you desire to accomplish, and then in all probability you will succeed in doing it..." -Henry Maudslay-