[SCOTI]

I have a 2wd, but FWIW I did use 73-80 front brake lines on my 68 when I swapped to discs. I used the lines from the master cyl all the way to the splice under the pass side of the cab where I cut it to the proper length & re-dbl. flared it.

I mounted the prop-valve in the stock location for the 73-up truck, not where my 68's was mounted originally & used the 73-up flex lines for the calipers & just mounted them in the correct 73-up location (the holes were already in the frame).