I'm starting this thread to consolidate information concerning frame interchange. Feel free to fill in with more helpful information or corrections.
Loren
As you may be aware, all body styles of the '65 Gran Sport used a fully boxed frame. The '64 - '66 convertible frames are the same with slight differences. The '66 frame may not have a welded on triangular tab on the front cross member at the lower front.
According to the sales information about the '65 GS, the rear cross member over the axle is suppose to be heavier. I have not confirmed that with a physical measurement.
All the mounting points will be the same for the three years.
The part number between the '65 GS frame and the '65 Special frame are different. This may be because of that difference.
'65 FRAME Gr.7.003 P/N 9780911 SPECIAL GRAN SPORT; 9780503 SPECIAL CONV. EXC. GRAN SPORT
'66 FRAME 1966 Buick Parts book, frame P/N 9783404 is used on Special & Skylark convertibles, as well as all GS models.
