Frame Rail Comparison

It was mentioned to me that the front rails for my 70, 340 Duster could possibly be the same as ones under other a/b/e body cars with the same style k-member. Is there any truth to this, and if so, which years and models would work. The left rail under my car is damaged. It is not rusted, and the rail caps that I've seen will not work for what I'm wanting to do. Any help with this will be greatly appreciated!