FINALLY GOT IT BACK!

A few of the various motors had the pistons matched to the bore to the hundred-thousandth, five decimal places. I've never seen a factory publication for anything other than the 426, but there's pics on the web of 440's and even 383's with painted letters on the side of the block, barely visible under the factory paint. If you look in a FSM that has the 426 specs, it's in the engine section. Under "Specifications" at the back, cylinder block bore. "A" is 4.24975, "B" is 4.25025, etc to "E" at 4.25175. It's a .002" range broken into 5 steps. If I had to guess, your 340 got assembled with the bores about .00125 on the big side. It might be .040" from the factory.

Like I said, this is just a guess.