Had this happen on my '67 Impala SS
The same thing happened on my 1967 Impala SS 327 - it was a broken motor mount on the right side. The engine would torque over, raise up and pull the linkage to the floor.
Dave / Believer45
'95 F250 power stroke 5 spd 4x2, mfg 3/95 in Kansas City, extended cab, long bed, 3:55 rears, open air filter, 285/75x16 Cooper Discoverer ATS tires, Putco master boss running boards, aluminum cap on bed, custom rear bumper (@350 lbs additional weight), scale weight full of fuel, me in it (285#) - steer 3420 drive 3160 gvw 6580, 222,000 miles on my way to a half million.