DMO,
When I first did my power brake conversion I still had drum brakes on all for corners. I later swapped in a 73 Disc brake front suspension. I used ALL the original brake lines & proportioning valve (Combination Valve) from the 73 C-10. I did however have to make a bracket to mount the proportioning valve in the 73 location. This was easy for me since at my work I have access to lots of scrap metal (stainless steel) and a welders.
Here's a link that gets into more detail as to what I did if that helps any at all.
http://67-72chevytrucks.com/vboard/s...d.php?t=703755