According to the 68 Plymouth service manual you don't use the rope method on Valiant models including the Barracuda.
I don't have my laptop connected to my scanner so I can't scan the page.
I'll try and type it out.
Windshield installation ( except Fury)
1)remove all old sealer and cement from original weatherstrip.
2)Apply sealer in fence and glass groove portions of weatherstrip. On Valiant models install filler strip in lower part of weatherstrip.
3)Apply 3/8 inch bead of sealer cement completely across cowl top panel lower windshield frame area.
4)Position weatherstrip lower section to tab area, starting at the corners installing over tabs and working toward center.
5)Install weatherstrip on fence at sides and upper opening. With hand pressure, seat weatherstrip fully on fence.
6)With an assistant , slide upper edge of glass into channel of weatherstrip.Use a fibre tool to force weatherstrip lip over glass.
7)Seat glass in weatherstrip, pound glass , with the palm of hand using an upward motion.
8)Insert a fibre tool between weatherstrip and glass, at either corner, slide tool across top, and completely around weatherstrip to seat glass in place.
9)Using a fibre tool and working across top, down the sides and over the bottom,force weatherstrip locking tab into lock position.
10)water test windshield area.
11)Install garnish mouldings, wiper arms and blades.
Hope this helps.
The back goes in the same way.