Purchased 1973 duster a few weeks ago need help

On your dragging brakes.
You changed to front lines.
But if some trash was in the system it could have "wedged" in the new lines.
I had this happen and it drove me crazy trying to figure it out.
When you step on the brakes the pressure expands the rubber and lets a piece of trash in there.
When you take your foot off the line contracts and does not let the pressure bleed off quickly.
It's a very small opening in the line.
You might want to jack the car up and check for the front wheels to turn freely after hitting the brakes.
Might be a wild goose chase too.