'73 Swinger brake drag

There are a few things that can cause this, at least some of which has been mentioned

1...The caliper pistons "help" being retracted due to the seals, which "walk" sideways and are supposed to spring back. So corroded calipers/ pistons, sticky, gummed up, or deteriorated / old caliper seals could cause this

2...If the master DOES have a residual pressure valve in the disk circuit, that might be a factor. The disk/ front brakes connect to the REAR port on the master

3.Someone mentioned hoses, but if the entire system is old, there may be restrictions. I would start by flushing it out.

4...Something could be gummed up in what IS your proportioning/ combination valve, as it IS a prop valve and also acts as a distro block and warning lamp switch. This is a piston that shuttles to activate (ground) the switch terminal

5..Make certain the master piston(s) are fully returning and not blocking pressure. You can see this by having someone manipulate the brake pedal while watching the fluid in the master. There should be small "spurts" of returning fluid on let-up in both halves of the master

All of these drag "some." All of these run "somewhat warm"