Why not do this RIGHT?

Replace the speakers with those you posted, they look good to me.
THEN....
Replace the amp with a modern aftermarket four channel amp.
THEN...
Replace the head unit with a modern four channel AM/FM head and run four more wires from the new head to the new amp, so you have real four channel audio with fader and EQ?

I admit it's more money, but its worth it. Ask me how I know!
(And this asinine dual coil speaker thing is......................... asinine. I swear, the things they did with these cars.....)