Brake line help

[Todersauce]

I have a 68 K20 it had 4 wheel drum brakes with what I assume is a stock brake system. I have a rebuilt front 78 Dana 44 open knuckle axle with disc brakes that I’m installing. I have installed new 4” lift springs. I’m also trying to install a 14BFF in the rear with disc brakes.

My issue is with the brake lines. The new calipers and stainless brake lines for the lift are 3/16” lines while the stock lines are ¼”. The old metal lines are, well old and when I opened them I found they were full of “mud” I have no clue what it is but I figure it is as easy to replace them then clean and repair them. I have called classic tube and another company and no one seems to make a replacement kit for the 4x4.

I think this is a common swap what did you guys do to make a safe brake system?