73 duster front brakes locking up when coming to a stop.

So in this pic , the top break line that goes to the rear of the master cylinder for the front brakes , correct or no

Yes.
If the master cyl has the largest reservoir closest to the firewll, that is the front disc brake reservoir goes to top center fitting on pic I posted.
Small reservoir goes to bottom of pic to single fitting, then single line out other side to rear brakes.
I say this cuz some masters have large front reserve for disc brakes, and are being sold with boosters for universal fit .
Cheers