Contained on my website are two things. First is a chart where one can determine the date of stamping of the engine when it was completed at Dearborn. This only works IF THE ENGINE NUMBER PAD AND THE ORIGINAL NUMBER ARE ON THE BLOCK...IF IT IS A RESTAMP, FORGET IT.
The second item is contained in the engine block data. This is a "guide" to go beyond the original stamped engine number (or if the original engine number is gone) by looking for specific things on and within the block itself. This will give you a approximate date of manufacture of the block in question.
Pluck
With a set of judging standards or the Ford Service Bulletins you could analyze your various parts and try to identify whether the majority is 30 or 31. Some differences are the front radius rod, front brake actuating arms, dashboard, emergency brake cross shaft, splash aprons and running boards, indented firewall mid 31, shocks and arms. These items all changed at various times throughout 30/31. This would also provide some engine insight as well.