Found: Early '68 340
My 68 340 and trans have the partal VIN# stamped at the rear I believe, where the trans bolts to the block, it's stamped in the bellhousing, also on the block near the same place? Or maybe the block # in on the rail, been awhile since I looked. Can't remember, just know my engine is from A 68 Cuda-S.
Also, I seen your 340 has X heads, so those are also correct for that year engine.