BINGO!!! http://www.angelfire.com/tx/lonestar...s/chassis.html
*1964-67 A-bodies used the same frame design, but different models and bodystyles utilized various body mounting, while all frames had a 115 inch wheelbase, which is similar to the 1955-57 Chevrolet.
*1968-72 frames had two different wheelbases, a 116 and 112 inch wheelbase. Sedans , station wagons, and utilities like the El Camino used a 116 inch frame, and the frame is interchangeable, except that the sedan had non-boxed rails.
http://www.angelfire.com/tx/lonestar...terchange.html And this area explains that the 70-72 Chevelle and Elky frontend do NOT interchange
................. pretty dam!n indepth site