Umpy is right, the frame where it bumps up over the rear wheels is the mid year Vettes Achilles Heel.
1964 is the least desireable of the mid year cars, 1963 had the split window, '65 disc brakes and a 396,
and of course '66 and '67 with the 427.
Having said that an appraisal is a must. I have a...