400's could be had with two or three freeze plugs...

All 400 blocks had bosses for 3 freeze plugs ...so look close

some BUT NOT all were like this....2 out of three plugs = 2bolt mains....

all three = 4bolt mains....this is not always true I have had them both ways....but they all have had bosses for all three plugs...

Also for engine ID codes...get the complete code from the water pump pad ( top left facing the water pump) and the call a Chevy dealership....

Tell them you have this engine and it has a busted head and need a replacement and want to order the RIGHT head but need to know exactly what engine you have..... walla...punch....enter...

You'll have the right answer... and not the best educated guess...I have done this for 20+ years and they have been spot on every time...by now I think they know it's me before they pick up the phone....Doc