Are you sure thats not a 3751841? Insted of 3751341, if it is then you have a 318/340 cast crank with 6 bolt flange. I have it listed as 62-97 318 and 68-73 340, and 63/69 273 all with cast crankshaft.
With the casting # that he gave it shows to be a cast crank, and a forged crank has a different casting #. This didn't mean that it came in the 340 engine, in these years but since it was the same casting as the 318 they just included it with the 340.
