Originally Posted by BEAST477
Did anyone count the number of freeze plugs on the side of the block? A 400 + .030 = 406 will have three freeze plugs per side all other small blocks have only two. Also a 406 is external balanced and should have an external balance dampener and flexplate. Should be easy enough to tell by getting underneath the van. You do have a floor jack and some jackstands don't you?
I believe some 400's have 2 freeze plugs as well. The 511 has 3 plugs for sure..Depends on the casting. I could be wrong though.
Balancer is the dead give away unless they claim it is an aftermarket crank balanced internally.
If you can read them I always look at the casting number of the block.