I am putting the brakes from 71-72 on my 1969 and decided to re-route the brake lines to make them attach the brake hoses at the front of the cross member. I recommend reading pjmoreland's post.
https://67-72chevytrucks.com/vboard/...d.php?t=823192
I bought inline tube front steel pre-bent brake lines for 71-72, and rear and front-to-rear steel pre-bent brake lines for 1969. The front set includes the rear brake lines that go from the master cylinder to the proportioning valve, and from the proportioning valve to the cross member, and from the cross member to the passenger side frame. The front-to-rear and rear brake line pre-bent for 1969 simply replace the old lines you have now on the 1969, if you are using the 1969 differential and other parts in the rear. Here is some more discussion about my journey.
https://67-72chevytrucks.com/vboard/...d.php?t=824884