I'd have ask how far up in the cylinder is the small sand pocket and how big is it, also do you have a way of pressure testing that cylinder to see if the hole is thru the cylinder. I've got a 2 bolt 377" and a 4 bolt 406" motor but i'm with Carl on this one without even reading the links he provided, i would NEVER sleeve a 400 blk, too many issues with head gaskets leaking and bolts pulling out.
If the pocket in down in the blk. and it's not thru i'd run it as is if it's narrower/smaller than the ring width.
JMO
Zip.