A 383 has 28 more inches than a 355. a 406 has 23 more inches that a 383.I was thinking of building a 383 for my 70 chevelle several years back and I ask a friend who owned one of the biggest speed shops in the state what he would do. This guy has personally built many Winston cup and bush grand national engines and anything and everything on the local level.His answer was one we've all heard many times before. ----THERE IS NO REPLACMENT FOR DISPLACEMENT.----I built a short rod 406 with the early chev stage one turbo heads.I can tell you one thing for sure, the more gear you take out of it the faster you will run.It has tons of torque but you wont be turning it too hard. I built another one for a friend . If I were going to be doing any serious racing it would deffinitly be a long rod motor . The short rod motor has the advantage to 4800RPM. Beyond that the long rod motor has the advantage and you can turn it harder. It seems you see a lot more articles on 383's than 406's . There might be something to that. This is just something else for you to consider.