OK, don't know how helpful this will be to anyone since it's possible no one else would be dumb enough to swap the wrong choke plate and shaft into their carbs, but the correct choke shaft and plate seems to have done the job. With it set at closed when cold, it opens all the way when fully warmed up. Will let it cool down now, and possibly make slight adjustment but I think it's really close now.
Here's the comparison of the two choke shafts. Correct one is visibly larger.
And new shaft and choke plate in the car, running, after fully warming up.
And if you want to hear how it sounds, I just now posted this You Tube video. (The springs on the floor behind the Barracuda are Eaton heavy duty rear springs for my 59 Dodge.) It sounds smoother and quieter in the video than it did when I was standing behind it. I put the cam in probably 20 years ago, when it still had the factory heads and exhaust manifolds. Could use more cam now, but I don't feel like tearing the motor apart to switch.