So far, no one has found documentation on any production changes, including DeAngelis, a mighty hunter of Ford information. A diamonds are based on the last production block with stronger rear wall and stronger bellhousing, but I don't think anyone has found anything further on them either. Somewhere there must be specifics on foundry and something that would indicate whether there were core changes...
Someone reporting in Secrets weighed a few blocks and got very mixed results...one of the diamonds was heavy, others not as I remember. Weighing is probably pretty dodgy, as overbores, jacket metal lost to rust, and weight added by water jacket crud would have to be accounted for.
I think they come with and without hard seats, and that probably depends on date and when Ford started using hard seats in the V8 productuion engines.
Almost all the B's I have found recently are diamonds. All of them, including one that still had wornout standard bore, had early B cranks, for whatever that might be worth!