The problem is that wiper design changed sometime in the 90's to 00's (IIRC) and now the blades are thinner front to back, causing them not to engage the tabs on our blade holders.
They also changed the metal stiffeners from an assembly that is crimped around the blade and onto a spring clip, to separate lengths of small stainless bar stock that are held in place by the blade holder tabs (again, that are now too wide).
I've found 16" refills at NAPA within the last few years that were MUCH cheaper than the ones advertised elsewhere for "classic cars".
Just the other day, I discovered a modern "beam" blade assembly that came off my 00' Dakota, that looks like it will fit the arm of my 73 (although I will need to fabricate a clip) and also clear the under-hood parking area.
That parking area clearance is another real bitch with modern blades. They are all too high, except for those mentioned above.