The only difference in the rear framerails, if I'm remembering right, the 70 rear rail's, on the right rear framerail there is an oval hole, on the inside and outside. Most 69 rail's do not have these hole's in them. You can weld them up, if need be. Beside's that,
they are 100% the same. Just like BBcoronet said, all is the same, except for the outer wheelhouse's.