I relocated the lines to the front of the crossmember on my '68, described here:
https://67-72chevytrucks.com/vboard/...d.php?t=823192
lolife99 commented on that thread that he has done a couple of disc brake conversions where he used the stock brake line mounting locations and had no problem. You might contact him and see how he did it. I think one factor might be the type of rims and tires you use. If you have big rims with low profile tires, I believe there will be more room for rear routed hoses to bulge outward when the rear of the tire turns in in the back