Ahh you figured it out
Your problem is the total advance is probably still too high. IIRC my stang was about 32-34???? Get a dial back timing light, that will allow you to measure the full advance curve by turning the knob to bring the mark back to zero, can read to 60+ degrees that way.
Changing the weights and springs will alter the rate the centrifigual advance comes on, not the total mech advance.
Like the other guys said, most aftemarket dist will have provisions to adjust the total mech advance. 10 deg initial timing is a good place to start with 20 deg advance. Go up from there till it pings, then go back 1 deg