I have a 69 Z11, 396 4spd with 57K miles. It is a great driver and fairly tight. In the past few months it has developed a front end shimmy/bounce around 45-50MPH. Before and after okay. I have recently replaced the OE polyglass with radials (this helped initially but it seems to be getting back to where it was before), balanced all tires, rotated all tires, aligned the front end, had the drive shaft checked for balance and replaced front wheel bearings. Car also has new rear end rear if any consolation. Mechanic says shocks look good, the car and front end are tight and could offer no additional suggestions. Any thoughts?