Cat Whisker/window Sweep 70 Challenger

Hi
I bought a set of Top cat whisker sweeps that I'm trying to install on my '70 Challenger door panels.
It looks like they clamp on the plastic edge.
The gap looks much too small to force them on sideways and they won't slide on from the end.
Any advice would be appreciated.
Thanks

i just bought the outers....the inners look impossible to get off the panel alone..no less trying to put new ones on.. top-cat is the best ones by far however..i had the repops brand first every clip broke trying to snap them in..good luck