Well----There's a little more to it than the apparent .006 differance between the official overbore size and what the block mikes---it is standard that the clearance is in the piston not the cylinder---other words a piston for bore size "X" are "X-.00Y"
example----a piston for the stated .040 over 396 would be 4.134- "Y" or probably about 4.130----a piston for a 4.140 bore would mike in at 4.140-"Y" or around 4.136ish

We only do finish bore sizes with pistons in hand----