[Tx Firefighter]

Here you go.

Everything that Jim said is true of the 71-72 factory disc brake trucks.

The issue is, on the pre 71 drum brake trucks, the tab where the brake line and hose join is behind the crossmember rather than in front of it like the disc trucks. No factory hose will work properly when converting the truck to discs.

You can either (1) convert the hard lines to run up to the front side of the crossmember and use factory 71-72 hoses

or

(2) like I did, pay Early Classics 60 bucks a pair for special hoses they sell. These hoses bolt to the factory drum brake hard line and bracket and also hook up to the disc calipers. It's a special hose that they've sourced that fixes all the problems.