I have been told that the 326 to the 400 are the same block just bored. Question is are the walls that thick to where you can bore a 326 to a 400? It would seem to me the water jacket would be way to far away in the 326 to be affective? Or way to thin in the 400 ? I guess what I am saying is I have a 326 and is it possible to make it a 400. Thanks  

Though all the Pontiacs blocks have the same external dimensions the internal dimensions are quite different.  The 326 can not be over bored to the 400(~.3" difference).  Even the Pontiac 350 had a greater bore by around .15", double what a recommended max over bore should be.  There are websites out there affirming this.