It really doesn't matter much what size the line is. The only time it makes a difference is if there's a lot of flow causing pressure drop with smaller lines. But a brake system is basically static, meaning that there isn't pressure loss in the lines, and pressure coming out of the wheel cylinders to the shoes is dependent on the area ratio of the master cylinder and wheel cylinder pistons.
I'd use what the original Huck cylinders used (probably 1/4" - that's what the Bendix system on my '51 used.)


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.