Ride quality even worse than expected. Advice welcome.

Sounds like a lot of 'stiffen it up' suspension parts.
If you have poly bushings as well, then that's the way it resonates bumps. 70-80 series tires are what these rode on stock, rubber bushings, natural body flex and sway.. if you want them to corner, you stiffen them up with aftermarket parts

You got that right. A lot of people don't realize just how much extra road vibration poly bushings transmit, but it's a lot. It doesn't bother some people. It would me if it was something I drove everyday. For a street car, I prefer high quality rubber any day.