Changing out Spades

I would simply cut one leg off the existing spade, and attach them, you will have plenty of contact surface. The other leg is to keep them from turning when you tighten them.

You could crimp a hook or a ring or a spade onto one leg of the existing spade.

https://www.amazon.com/wire-connectors/s?k=wire+connectors

maybe better quality than these, just to show the idea. at the end, all you need is a good connection that won’t loosen by itself.

after all, look at the size of the wires inside these speakers

You would be shocked at the small gauge used by all speaker makers in the 50’s and 60’s, inside the models that made them FAMOUS!

In the end, it goes to the tiny wire wrapped around the coil.

Your speakers have the raised ridges (like vintage McIntosh or Fisher) to separate each spade or ring, and those ridges keep a single leg spade from rotating while tightening.

Another idea is to make short jumpers, proper size spade for the speaker, and a screw terminal sized for the cable spades. Think resale, this might keep the spades intact.

You might like these

https://www.transparentcable.com/products/transparent-spade-to-mini-bar-spade-adapter

$80. bucks never killed anybody" (watch the movie 'used cars')

Maybe I missed something on my quick read, but it would make far more sense to replace the oddball terminals on your speakers with a high quality binding post for your spades.  I would never re-terminate these cables--too many ways to screw it up.  Adapters are often inferior alloys that are total nonstarter for me.

You could install the new posts in parallel with the original ones so both could be used.  Connect the proper wires to your new posts and then use a high quality jumper wire (neotech) to go back to the original terminal.