There's at least one aftermarket frame available for the following cars. Since they were all listed together, some level of interchangeability is implied.
1964-1972 GM A-Body Chevelle, Malibu, GTO, Lemans, Tempest, Cutlass, 442, Skylark GS
For some unknown reason, I keep thinking there were some slight wheelbase differences (112" & 116") depending on the sub-model, though that may be associated with whether the vehicle in question was a station wagon or an El Camino.
Norm