CU-gator........iff'n I remember the Ferguson codes, 12-AO is 12" beam. This is from John Farnsworth's "Ferguson Implements and Accessories" book.
Now lets see iff'n you are asking the right question. Plow beam is the heavy cast loop; common replaceable parts: the shin is the vertical cutting part; share is the horizontal cutting part; moldboard is the long swoopy turn-over part.
I have a 2000 catalog from Central Tractor in Iowa that lists: shin = $9.49
share = $7.49
moldboard = $64.99