Somewhere I'd heard that the 2 door and 4 door used the same frames in 1964 and 65. That seems odd to me, as I would think the 4 door would need to be longer as it is in 68-72. Can anybody confirm for me if they're the same or different? John

 

All 1964-67 A-body cars used the same 115" wheelbase except the Vista Cruiser and Buick SportWagon (which were 120"). Convertible frames were fully boxed. Non-convert frames were open-section C-channel. There was a "heavy duty frame" option in some years which was simply the boxed convertible frame under the hardtop body.

By the way, the 78-88 G-body cars similarly use the same wheelbase (108" in that case) for all models (2dr, 4dr, and wagon), except for the El Camino (which is 119")

 

Option F35 ($12.53 in 1966), the HD frame, was available on sedans also. In the mid 80s I found a 1967 2 door sedan Turnpike Cruiser in the boneyard with F35.