I know the difference between a convert frame and a coupe. Will a el camino frame fit under a convert. If not what is the difference in length between a chevelle and an el camino. Thanks in advance

What year?, that determines length and wheelbase. Regardless of the year, an El Camino frame will not be a direct fit to a convertible.

sorry 68-72. I figured the elco frame will be longer but in which part is it longer the mid section, the rear, or the front. Thanks again

It's 4" longer in the middle, 6-1/4" longer in the rear, and the very back part of the frame is flat, rather than curving up about 1" on all models except wagon and camino.