2128869 Forged Crank 340, 273 318? Losing my mind!

I am trying to figure out if a forged crank with casting number 2128869 is for a 340, 318, or 273. As far as I am aware they all look identical, please please correct me if there is a way to tell the difference. The problem I am having:

1. http://www.mopar1.us/casting.html list 2128869 casting number as a 68-72 Forged 340 Crank or a 67-75 318 Crank. I am assuming some of the early 318 cranks were also forged?

2. In Don Taylor's book "How to Rebuild a Small Block Mopar" He has the following chart for crank casting numbers. The only place the 2128869 number shows up is as a forged 273.

So is there anyway to determine if a Crank with casting number 2128869 is a forged 340 crank?