Need help IDing my 340 motor

I decoded my VIN (VN29H1E103516) and it matches what I found on my fender tag for a 1971 340 4bbl Duster. My transmission matches the last 4 of the VIN. My question is how do I know this is a matching engine? I thought it was matching as I found a 2780930-340-3 on the block drivers side and found that to be a LA family 1968-73….but the number on the pax side above the oil pan and below the water drain hole appears to be 019754 9. The last 9 looks a little smaller. I've bought this car around 1982 and the engine and tranny had been rebuilt by the dealer in Chinook, MT. Any help would be appreciated as I'm a novice!!