71 Swinger that lost it's TA block somehow-$2500

After getting the car up in the air and getting fully filthy I regret to report the nay-sayers were right, it's a 2780930-S.

Anyone know what the S designates?

Now I wonder if I somehow didn't get my own block back in that rebuild, and how it was the "thicker" web skirts were pointed out to me by someone..or why they would want me to think I had something I didn't.
I had no reason to expect such a thing to happen but I cannot argue with what I see today. I can only argue with my memory.
I'll be asking a lower price now for sure, and apolgize for posting with false hopes.

Does anyone know of a case where a switcheroo was pulled on an engine block in a rebuild? Or is that unheard of?