There was an even later 400 that had smooth block sides, looks just like any other sbc. I have a 4 bolt 400 but it has weak decks, don't know if this was chronic or not but it has three freeze plugs and it's been my experience that the early three plug blocks had weaker decks. We champhered down one thread in the head bolt holes, used studs, and dead soft copper head gaskets for the alcohol engines which got us by. The later blocks held much better. Race engines are usually internally balanced but a sure give away on original engines is the big notch out of the harmonic balancer. Be SURE to use the 400 balancer and 400/454 flywheel-flex plate or it will shake so bad you can't see anything in the rear view mirror.
