Soff-Seal doesn't make the window belt weatherstips. I have a Regal I im restoring and have purchaced all the other seals from JEG'S. They are all Soff-Seal products, and the price is great(Roofrail:$59.99, Doors:$59.99, Trunk:$21.99). They even came with all the mounting hardware, like little plastic push-tacks, as well as molded mounting tabs just like the factory.
Haven't installed anything yet, though...Everyone I know (some I don't) says they have never had trouble with installation, or leaks from Soff-Seal products, even my uncle who restores cars.