if it has casting # it could be a late 340 crank like mid 72 or 73 (they were cast)look at the parting line in middle , in your pics you see it , its like 7/16in wide where on a casting it will be thinner like 1/16th...
Sorry just assumed it maybe was cast but reread your post and saw you mentionned FORGED , checked those #s too and cast cranks would have different # cast in them. my bad...
