I have a '63 GMC with the frame around the door windows. I'm replacing the window channel that goes in the top and rear of the door. The original was corrugated metal with mohair fabric around it. Mine had clips cross-ways to the window channel that popped into the door frame. The repro channel doesn't have these clips. How do you secure the new channel to the door frame? do they just push in? do you screw it to the frame?