A lot of Pacers came with the 388 casting numbered block for some reason, usually with 041 heads (occasionally with 186/300 horse heads). By the time the first Pace cars were built in the last week or so of February, Norwood had long since planted the VIN on the side of the block, in the flat rough cast area right above the oil filter as was mentioned. Not the easiest thing to spot, but usually there. Casting dates align normally, but the casting number is a strong clue as to originality (or the possibility of).
Just my opinion -
Regards,
Steve