Up thru 1968 all you will find stamped in on a body is a manufacturing sequence number, and nothing on the engine typically except its size stamped in.
Starting in 1969 the last 8 of the vin would be stamped in 2 locations on the body, also on a machined pad on the engine usually close to the oil pan rail, and on a machined pad on the transmission, pan rail on automatic, and on a specially cast in pad on passenger side for manual. This was for anti theft, and theft recovery purposes.
On the body, locations vary as to the location on the back of the car, however on the front, it's usually always the top of the radiator support on the LH side. Factory would cover em up with a yellow mopar antifreeze sticker On your Dart probably the LH trunk drip rail in the back under the weather stripping. That's where I found the rear body numbers on my sons 69 notchback.
On dusters, dart sports, and demons I could be wrong, but I believe those numbers were stamped in the speaker deck.