Wow....I've made customer wiper blade for customers many times. Are these wipers for a Dart? My 70 B-body wiper blade frames don't come apart from the wiper arms themselves, so re-fill is my only option.

You probably already figured this out, but just cut the blades themselves with a razor & cut the metal inserts along the sides with snips & "done". On my 70, I have a little tab at the end of the wiper backing ("bracket" I think you call it) that I have to "snake" the refill past... sort of a little metal tab that keeps the refill from sliding out the end.

If YOUR wiper arm has a "U-hook" at the end of it, then almost all modern replacement wipers (blade + backing) will fit. "Some" cars need a little plastic adapter/insert for odd-sized "U-hooks" (Mercedes & BMW are like this a lot) and O'Reilly has a case of free adapters behind the counter.