Is that for a front disc conversion? Because that hard to soft union is at the rear of the crossmember like on a drum brake setup. The hard to soft union on a 71-72 front disc rig has the union on the front of the crossmember.
When I swapped all my 1972 stuff to a 1969 frame I already had the brake lines (kit from inline tube) already ran for my stock disc brake setup on a 1972 frame. So I had to cut the soft brake line tabs off of the front of my 1972 crossmember and weld them onto the 1969 crossmember.
Not sure if that is your issue or not. But here is a post from my build thread about it:
http://www.67-72chevytrucks.com/vboa...&postcount=157
Gary