I'm purdy sure thats a 39
04815. Makes it a 396,402...cast, nodular iron according to Mortec
and others. Look closely at the other "8" and see the difference in the center of the digits. The "8" is straight across where the "9" is slightly slanted.
As far as 'ringing' a crank to tell if it's forged or cast, unless you have a hell of an ear for it- as in you handle cranks daily- you can't tell cast from forged. If you have two similar cranks, one forged and one cast, they'll sound different but unless you know which is which and ring them at the same time, all you'll know is they ring differently.